Leonardo Pisano Bigollo (1170-1250) a.k.a. „Fibonacci”
Italian Catholic mathematician who advocated the use of the numeral system that is still used today (1,2,3,4,5,6,7,8,9,0) and famed for coming up with the „Fibbonacci Sequence.”
Robert Grosseteste (c. 1175-1253)
English Catholic Bishop who developed mathematical physics, put forward the first known wave theory of light, and advocated the use of controlled experiments (which led to the modern scientific method).
Albertus Magnus (1193/1206-1280) a.k.a. „Albert the Great”
German Catholic Bishop (and Dominican Friar) who, in addition to writing extensively on logic, psychology, zoology, mineralogy, metaphysics, meteorology, astronomy, geography, chemistry, and psychiology, was the first person to isolate a new element (arsenic) in thousands of years (he is also the patron saint of the Natural Sciences).
Theodoric Borgognoni (1205-1298)
Italian Catholic Bishop (and Dominician Friar) who invented an anesthesia which was one of the most widely used anesthesia up until the nineteenth century.
Roger Bacon (1214-1294)
English Franciscan Friar often credited with inventing the scientific method.
Taddeo Alderotti (1215-1295)
Italian Catholic physician who developed fractional distillation.
Ramon Llull (c. 1232-1315), a.k.a. Ramond Lully
Spanish Catholic (and Franciscan tertiary) who invented a device considered to be the first computer, earning him the title the „Father of Computer Science” (he was beautified by Pope Pius IX in 1857).
Theodoric of Freiberg (c.1250–c.1310)
German Catholic priest (and Dominican friar) who gave the first correct explanation of rainbows.
Thomas Bradwardine (1290-1349)
English Catholic Archbishop, physicist, and mathematician who came up with the Law of Falling Bodies (hundreds of years before Galileo).
Jean Buridan (c. 1300-1358)
French Catholic priest and scientist who developed an early theory of inertia and momentum.
Guy de Chauliac (1300-1368)
French Catholic physician who served as the Pope’s physician and is one of the scientists considered to be the „Father of Modern Surgery.”
Nicole Oresme (1320-1382)
French Catholic Bishop who invented abstract graphing (pre-Cartesian but which seemed to inspire Descartes' system), first use of fractional components, the first to write about the divergence of harmonic series, and the first to write about general curvature (and, relatedly, the first to discover the curvature of light through atmospheric refraction).
Filippo Brunellescchi (1377-1446)
Florentine Catholic engineer, architect, and artist who discovered geometric optical linear perspective (and also designed the largest masonry dome in the world, still the biggest to this day).
Nicholas of Cusa (1401–1464)
German Catholic Bishop (and Cardinal) who developed the concept of the infinitesimal in mathematics, advanced theories regarding relative motion, and conducted first formal modern experiment in the history of biology (it pertained to how plants received nourishment from air).
Leon Battista Alberti (1404-1472)
Italian Catholic priest whose great talents earned him the titles „Father of Modern Architecture,” „Father of Modern Surveying,” and „Father of Western Cryptography.”
Johannes Muller von Konigsberg (1436-1476)
German Catholic Bishop, astronomer, and mathematician considered by many as the „Father of Modern Astronomy” and was among the first to use symbolic algebra.
Leonardo da Vinci (1452-1519)
Italian Catholic scientist who, in addition to writing extensively about anatomy, geology, astronomy, and botany (and many others), is the person credited with starting the Scientific Revolution.
Johannes Widmann (1460-1498)
German Catholic mathematician who, among other things, came up with the plus sign (+) and minus sign (-) still used today.
Martin Waldseemüller (c.1470-1520)
German Catholic cartographer, considered by some as the „Father of Modern Geography” (he was the one to coin the term „America” to describe the continent(s) of the western hemisphere).
Nicolaus Copernicus (1473-1543)
Polish Catholic cleric, famous for formulating a heliocentric model of the universe (and, contrary to popular belief, was NOT persecuted by the Church at all).
Vannoccio Biringuccio (1480-1539)
Italian Catholic metallurgist considered the „Father of the Foundry Industry” and the first scientist to isolate the element Antimony.
Georgius Agricola (1494-1555)
German Catholic scientist known as the „Father of Mineralogy.”
Niccolò Fontana Tartaglia (1499/1500-1557)
Italian Catholic mathematician and engineer who came up with the formula to solve cubic equations and the first to apply mathematics to projectiles, earning him the title the „Father of Ballistics.”
Gerolamo Cardano (1501-1576)
Italian Catholic mathematician, physician, and astronomer who was the first to make systematic use of numbers less than zero.
Andreas Vesalius (1514-1564)
Flemish Catholic physician, considered to be the founder of the modern study of human anatomy.
Realdo Colombo (c. 1516-1559)
Italian Catholic anatomist who discovered the pulmonary circuit, which lead to the discovery of the circulation of blood.
Lodovico Ferrari (c. 1522-1565)
Italian Catholic mathematician who came up with the formula to solve quartic equations.
Gabriele Falloppio (1523-1562) a.k.a. „Fallopius”
Italian Catholic cleric, anatomist, and physician, after whom the Falloppian Tube of the reproductive system is named (as well as the aquaeductus Falloppii).
Hieronymus Fabricius (1537-1619)
Italian Catholic anatomist, considered the „Father of Embryology.”
José de Acosta (1540-1600)
Spanish Catholic priest (and Jesuit) who gave the first detailed description of the geography and culture of the New World and is also considered a pioneer of the Geophysical Sciences.
François Viète (1540-1603)
French Catholic mathematician, considered to be the „Father of Modern Algebra.”
Gaspare Tagliacozzi (1545-1599)
Italian Catholic surgeon who pioneered plastic and reconstructive surgery (successfully performing skin autografts).
François d’Aguilon (1546-1617)
Belgian Catholic priest (and Jesuit) who laid the foundation for Prospective Geometry (he was the first to use the term „stereographic”).
Anselmus de Boodt (1550-1632)
Flemish Catholic scientist who wrote the first definitive work on modern mineralogy.
Christoph Scheiner (1573/1575-1650)
German Catholic priest (and Jesuit), physicist, and astronomer who accomplished the first systematic study of sunspots.
Marin Mersenne (1588-1648)
French Catholic theologian, considered the „Father of Acoustics.”
René Descartes (1596-1650)
French Catholic mathematician who invented the Cartesian coordinate system and analytical geometry.
Giovanni Battista Riccioli (1598-1671)
Italian Jesuit priest and astronomer who was the first to measure the acceleration due to gravity of falling bodies (and the one to devise the current modern scheme of lunar nomenclature).
Pierre de Fermat (1601-1665)
French Catholic mathematician whose work led to infinitesimal calculus (famous for „Fermat’s Last theorem”).
Evangelista Torricelli (1608-1647)
Italian Catholic physicist and mathematician who invented the barometer and after whom the Torr unit is named (which measures pressure).
Giovanni Alfonso Borelli (1608-1676)
Catholic Italian physicist and mathematician, considered founder of Biomechanics.
Francesco Maria Grimaldi (1618-1663)
Italian Catholic priest (and Jesuit priest) who was the first to make accurate observation on the diffraction of light (and was the one to coin the term „diffraction”).
Jean Picard (1620-1682)
French Catholic priest and astronomer who was the first person to measure the size of the earth to a reasonable degree of accuracy (and is one of the scientists considered to be the „Father of Modern Astronomy”).
Blaise Pascal (1623-1662)
French Catholic mathematician and physicist who laid the foundation for probability theory, invented an early calculator/computer, and made important theories and experiments regarding pressure and vacuums (the unit “pascal” is named after him).
Ferdinand Verbiest (1623-1688)
Flemish Catholic priest (and Jesuit) who built the first steam-powered vehicle.
Giovanni Domenico Cassini (1625-1712)
French Catholic mathematician and astronomer who discovered the first four moons of Saturn.
Marcello Malpighi (1628-1694)
Italian Catholic doctor who founded Comparative Physiology and is considered the „Father of Microscopic Anatomy” (and was a physician and personal friend of Pope Innocent XII).
Francesco Lana de Terzi (1631-1687)
Italian Catholic priest (and Jesuit), considered the „Father of Aviation/Aeronautics.”
Nicolas Steno (1638-1686) a.k.a. Niels Stensen
Danish Catholic Bishop, considered the Founder of Modern Geology and Stratigraphy (he was beautified by Pope John Paul II in 1988).
Giovanni Girolamo Saccheri (1667-1733)
Italian Jesuit mathematician who was the first in the modern age to pioneer into non-Euclidean geometry.
Giovanni Domenico Santorini (1681-1737)
Italian Catholic anatomist known as the „Father of Histology” (the study of the microscopic structures of tissue).
Giovanni Battista Morgagni (1682-1771)
Italian Catholic anatomist, considered the „Father of Modern Anatomical Pathology.”
Ruđer Josip Bošković (1711-1787)
a.k.a. Roger Joseph Boscovich
Italian/Slavic Catholic priest (and Jesuit) who developed modern atomic theory and the theory of relativity (200 years before Einstein, according to Tesla).
Andrew Gordon (1712-1751)
Scottish Catholic (and Benedictine Monk) who invented the first electric motor.
Antonio de Ulloa (1716-1795)
Spanish Catholic scientist who was the first to discover and isolate the element Platinum.
Maria Gaetana Agnesi (1718-1799)
Italian Catholic mathematician who wrote the first book discussing both differential and integral calculus (and the most important woman in mathematics for over a millenium, earning her great honor from the Pope).
Lazzaro Spallanzani (1729-1799)
Italian Catholic priest who was the first to come with the theory of animal echolocation (and is one of the scientists considered to be the „Father of Modern Biology”).
Luigi Galvani (1737-1798)
Italian Catholic physician, physicist, and biologist who pioneered the field of bioelecricity/bioelectromagnetics (the terms „galvanism” and „galvanization” are named after him).
Charles-Augustin de Coulomb (1736-1806)
French Catholic physicist who came up with the definition of the electrostatic force of attraction and repulsion (the SI unit of electric charge called the „coulomb” was named after him).
Antoine Lavoisier (1743-1794)
French Catholic chemist, considered the „Father of Modern Chemistry,” coming up with the first table of elements (and invented the terms „oxygen” and „hydrogen”), theorized that mass always stays the same, and was one of the main people to come up with the metric system (and he defined the unit that was later termed the „kilogram,” which is what grams would be based off of).
Alessandro Volta (1745-1827)
Italian Catholic physicist who invented the battery and after whom „voltage” is named (and accordingly the unit „volts”).
Giuseppe Piazzi (1746-1826)
Italian Catholic priest, mathematician, and astronomer who discovered and named the dwarf planet Ceres (the largest asteroid in the solar system).
Pierre André Latreille (1762-1833)
French Catholic priest and zoologist, considered the „Father of Modern Entomology” (the study of insects).
Louis Nicolas Vauquelin (1763-1829)
French Catholic chemist who discovered the elements Beryllium and Chromium (and discovered the first amino acid, namely asparagine).
Jean-Baptiste Biot (1774-1862)
French Catholic physicist, astronomer, and mathematician who made important breakthroughs regarding the polarization of light, magnetism, and electricity (the “biot” unit is named after him, which measures electric current).
André-Marie Ampère (1775-1836)
French Catholic physicist, founder of the science of Electromagnetism and after whom the unit „ampere” (i.e. „amps”) is named (he also discovered the element Fluorine).
Joseph Louis Gay-Lussac (1778-1850)
French Catholic chemist and physicist who discovered the element Boron (and came up with Gay-Lussac’s Law regarding the volumes of gases undergoing reaction at constant pressure and temperature).
René Laennec (1781-1826)
French Catholic physician who invented the stethoscope (in addition to advancing the understanding of many widespread diseases).
Bernard Bolzano (1781-1848)
Bohemian Catholic priest and mathematician who gave the first purely analytical proof of the fundamental theorem of algebra.
René Just Haüy (1783-1822)
French Catholic Priest who is considered the „Father of Modern Crystallography.”
Michel Eugène Chevreul (1786-1889)
French Catholic chemist who was a pioneer in gerontology (the study of aging).
Joseph Fraunhofer (1787-1826) a.k.a. Ritter von Fraunhofer
German Catholic optician who discovered Fraunhofer lines in the Sun’s spectrum, laying the foundation for spectrum analysis.
Augustin-Jean Fresnel (1788-1827)
French Catholic engineer and physicist who significantly developed the study of wave optics (establishing „Fresnel Equations,” which describe the behavior of light moving between media of differing refractive indices).
Augustin-Louis Cauchy (1789-1857)
French Catholic mathematician, after which more concepts and theorems are named than any other mathematician.
Ányos Jedlik (1800-1895)
Hungarian Catholic priest, considered the father of the dynamo and electric motor.
Francesco de Vico (1805-1848)
Italian Catholic priest (and Jesuit) and astronomer who discovered the six new comets, as well as the gaps between Saturn’s rings (a lunar crater and a major asteroid are named after him).
Theodor Schwann (1810-1882)
German Catholic physiologist who founded the theory of the cellular structure of animal organisms (he also coined the term „metabolism”).
Urbain Le Verrier (1811-1877)
French Catholic astronomer and mathematician who was the person who discovered the planet Neptune.
Louis René Tulasne (1815-1885)
French Catholic botanist who discovered pleomorphism in fungi (the ability to assume radically different forms) and earned the title the „reconstructor of mycology” (the study of fungus).
Ignaz Semmelweis (1818-1865)
Hungarian Catholic physician whose work in antiseptic methods earned him the title the „Father of Infection Control” (also gaining the title the „Savior of Mothers” for the resulting lives saved from childbirth).
Pietro Angelo Secchi (1818-1878)
Italian Catholic priest (and Jesuit), considered the „Founder of Astrophysics” for developing the first system of stellar classification (and was the first to scientifically assert that the sun is a star).
Hippolyte Fizeau (1819-1896)
French Catholic physicist who was the first to measure the speed of light on earth.
Léon Abel Provancher (1820-1892)
Canadian Catholic priest, considered the „Father of Natural History in Canada” for discovering and describing thousands of new species of insects and wrote the first French-language scientific journal in Canada’s history.
Eugenio Barsanti (1821-1864)
Italian Catholic priest and engineer who invented the internal combustion engine.
Ignacy Łukasiewicz (1822-1882)
Polish Catholic scientist who discovered how to distill petroleum into kerosene and invented kerosene lamps, the first modern street lamps, and the first modern oil well and oil refinery, which started the Oil Revolution (he was honored by the Pope for his scientific accomplishments).
Gregor Mendel (1822-1884)
Austrian Catholic priest (and Augustinian monk) and scientist who founded the science of Genetics.
Louis Pasteur (1822-1895)
French Catholic chemist, considered the „Father of Microbiology” and the founder of bacteriology (and invented „pasteurization,” which was named after him).
Jean-Baptiste Carnoy (1836-1899)
Belgian Catholic Priest who founded the science of cytology (the study of cells).
John Philip Holland (1840-1914)
Irish Catholic engineer who developed the first practical submarine (many submarines are named after him).
Édouard Branly (1844-1940)
French Catholic physicist who invented the first sensitive device for detecting radio waves.
Wilhelm Röntgen (1845-1923)
German Catholic physicist who discovered X-Rays (he won a Nobel Prize for this).
Giuseppe Mercalli (1850-1914)
Italian Catholic priest and volcanologist who developed a way to measure the magnitude of earthquakes (the Richter scale was based on this).
Henri Becquerel (1852-1908)
Catholic French physicist who discovered radioactivity (he won a Nobel Prize for this), resulting in his name becoming the unit for the measurement of radioactivity (the „becquerel” unit).
Jokichi Takamine (1854-1922)
Japanese Catholic chemist (and immigrant to the United States), considered the „Father of American Biotechnology.”
Frederick Odenbach (1857-1933)
American Catholic priest (and Jesuit) whose study of earthquakes made seismology known as „The Jesuit Science.”
Roberto Landell de Moura (1861-1928)
Brazilian Roman Catholic priest and scientist who demonstrated the first wireless radio broadcast of a human voice.
Karl Landsteiner (1868-1943)
Catholic Austrian biologist who first categorized the main blood groups (Type A, B, AB, etc.).
Alexis Carrel (1873-1944)
French Catholic biologist who invented the perfusion pump, making organ transplants possible (he won a Nobel Prize for this).
George de Hevesy (1885-1966)
Hungarian Catholic radiochemist who discovered the element Hafnium (he won a Nobel Prize for this).
Georges Lemaître (1894-1966)
Belgian Catholic priest, physicist, and astronomer who first proposed the theory of the Big Bang (which Einstein famously disagreed with until Lemaître scientifically defeated his objections).
(A much longer list of Catholic Scientists can be found here on Wikipedia)
List of Catholic churchmen-scientists
This is a list of Catholic churchmen  throughout history who have made contributions to science. These churchmen-scientists include Nicolaus Copernicus, Gregor Mendel, Georges Lemaître, Albertus Magnus, Roger Bacon, Pierre Gassendi, Roger Joseph Boscovich, Marin Mersenne, Bernard Bolzano, Francesco Maria Grimaldi,Nicole Oresme, Jean Buridan, Robert Grosseteste, Christopher Clavius, Nicolas Steno, Athanasius Kircher, Giovanni Battista Riccioli, William of Ockham, and others listed below. The Catholic Church has also produced many lay scientists and mathematicians.
The Jesuits in particular have made numerous significant contributions to the development of science. For example, the Jesuits have dedicated significant study to earthquakes, and seismology has been described as „the Jesuit science.” The Jesuits have been described as „the single most important contributor to experimental physics in the seventeenth century.” According to Jonathan Wright in his book God’s Soldiers, by the eighteenth century the Jesuits had „contributed to the development of pendulum clocks, pantographs, barometers, reflecting telescopes and microscopes, to scientific fields as various as magnetism, optics and electricity. They observed, in some cases before anyone else, the colored bands on Jupiter’s surface, the Andromeda nebula and Saturn’s rings. They theorized about the circulation of the blood (independently of Harvey), the theoretical possibility of flight, the way the moon effected the tides, and the wave-like nature of light.”
- José de Acosta (1539–1600) – Jesuit missionary and naturalist who wrote one of the first detailed and realistic descriptions of the new world
- François d’Aguilon (1567–1617) – Belgian Jesuit mathematician, architect, and physicist, who worked on optics
- Lorenzo Albacete (1941–2014) – priest, physicist, and theologian
- Albert of Castile (c. 1460-1522) – Dominican priest and historian.
- Albert of Saxony (philosopher) (c. 1320–1390) – German bishop known for his contributions to logic and physics; with Buridan he helped develop the theory that was a precursor to the modern theory of inertia
- Albertus Magnus (c. 1206–1280) – Dominican friar and Bishop of Regensburg who has been described as „one of the most famous precursors of modern science in the High Middle Ages.” Patron saint of natural sciences; Works in physics, logic, metaphysics, biology, and psychology.
- Giulio Alenio (1582–1649) – Jesuit theologian, astronomer and mathematician; was sent to the Far East as a missionary and adopted a Chinese name and customs; wrote 25 books, including a cosmography and a Life of Jesus in Chinese.
- José María Algué (1856–1930) – priest and meteorologist who invented the barocyclonometer
- José Antonio de Alzate y Ramírez (1737–1799) – priest, scientist, historian, cartographer, and meteorologist who wrote more than thirty treatises on a variety of scientific subjects
- Francesco Castracane degli Antelminelli (1817–1899) – priest and botanist who was one of the first to introduce microphotography into the study of biology
- Giovanni Antonelli (1818–1872) – priest and astronomer who served as director of the Ximenian Observatory of Florence
- Luís Archer (1926-2011) – Portuguese molecular biologist and editor of the journal Brotéria from 1962 to 2002
- Nicolò Arrighetti (1709–1767) – Jesuit who wrote treatises on light, heat, and electricity
- Mariano Artigas (1938–2006) – Spanish physicist, philosopher and theologian
- Giuseppe Asclepi (1706–1776) – Jesuit astronomer and physician who served as director of the Collegio Romano observatory; the lunar crater Asclepi is named after him
- Roger Bacon (c. 1214–1294) – Franciscan friar who made significant contributions to mathematics and optics and has been described as a forerunner of modern scientific method
- Bernardino Baldi (1533–1617) – abbot, mathematician, and writer
- Eugenio Barsanti (1821–1864) – Piarist, possible inventor of the internal combustion engine
- Bartholomeus Amicus (1562–1649) – Jesuit, wrote on philosophy, mathematics, astronomy, and the concept of vacuum and its relationship with God
- Daniello Bartoli (1608–1685) – Bartoli and fellow Jesuit astronomer Niccolò Zucchi are credited as probably having been the first to see the equatorial belts on the planet Jupiter
- Joseph Bayma (1816–1892) – Jesuit known for work in stereochemistry and mathematics
- Giacopo Belgrado (1704–1789) – Jesuit professor of mathematics and physics and court mathematician who did experimental work in electricity
- Michel Benoist (1715–1774) – missionary to China and scientist
- Mario Bettinus (1582–1657) – Jesuit philosopher, mathematician and astronomer; lunar crater Bettinus named after him
- Giuseppe Biancani (1566–1624) – Jesuit astronomer, mathematician, and selenographer, after whom the crater Blancanus on the Moon is named
- Jacques de Billy (1602–1679) – Jesuit who has produced a number of results in number theory which have been named after him; published several astronomical tables; the crater Billy on the Moon is named after him
- Paolo Boccone (1633–1704) – Cistercian botanist who contributed to the fields of medicine and toxicology
- Bernard Bolzano (1781–1848) – priest, mathematician, and logician whose other interests included metaphysics, ideas, sensation, and truth
- Anselmus de Boodt (1550–1632) – Canon who was one of the founders of mineralogy
- Theodoric Borgognoni (1205–1298) – Dominican friar, Bishop of Cervia, and medieval Surgeon who made important contributions to antiseptic practice and anaesthetics
- Christopher Borrus (1583–1632) – Jesuit mathematician and astronomy who made observations on the magnetic variation of the compass
- Roger Joseph Boscovich (1711–1787) – Jesuit polymath known for his contributions to modern atomic theory and astronomy and for devising perhaps the first geometric procedure for determining the equator of a rotating planet from three observations of a surface feature and for computing the orbit of a planet from three observations of its position
- Joachim Bouvet (1656–1730) – Jesuit sinologist and cartographer who did his work in China
- Michał Boym (c. 1612–1659) – Jesuit who was one of the first westerners to travel within the Chinese mainland, and the author of numerous works on Asian fauna, flora and geography
- Thomas Bradwardine (c. 1290–1349) – Archbishop of Canturbury and mathematician who helped develop the mean speed theorem; one of the Oxford Calculators
- Martin Stanislaus Brennan (1845–1927) – priest and astronomer who wrote several books about science
- Henri Breuil (1877–1961) – priest, archaeologist, anthropologist, ethnologist and geologist
- Jan Brożek (1585–1652) – Polish canon, polymath, mathematician, astronomer, and physician; the most prominent Polish mathematician of the 17th century
- Louis-Ovide Brunet (1826–1876) – priest, one of the founding fathers of Canadian botany
- Ismaël Bullialdus (1605–1694) – priest, astronomer, and member of the Royal Society; the Bullialdus crater is named in his honor
- Jean Buridan (c. 1300 – after 1358) – priest who formulated early ideas of momentum and inertial motion and sowed the seeds of the Copernican revolution in Europe
- Roberto Busa (1913–2011) – Jesuit, wrote a lemmatization of the complete works of St. Thomas Aquinas (Index Thomisticus) which was later digitalized by IBM
- Niccolò Cabeo (1586–1650) – Jesuit mathematician; the crater Cabeus is named in his honor
- Nicholas Callan (1799–1846) – priest and Irish scientist best known for his work on the induction coil
- John Cantius (1390–1473) – priest and Buridanist mathematical physicist who further developed the theory of impetus
- Jean Baptiste Carnoy (1836–1899) – priest, has been called the founder of the science of cytology 
- Giovanni di Casali (died c. 1375) – Franciscan friar who provided a graphical analysis of the motion of accelerated bodies
- Paolo Casati (1617–1707) – Jesuit mathematician who wrote on astronomy, meteorology, and vacuums; the crater Casatus on the Moon is named after him; published Terra machinis mota (1658), a dialogue between Galileo, Paul Guldin and father Marin Mersenne on cosmology, geography, astronomy and geodesy, giving a positive image of Galileo 25 years after his conviction.
- Laurent Cassegrain (1629–1693) – priest who was the probable namesake of the Cassegrain telescope; the crater Cassegrain on the Moon is named after him
- Louis Bertrand Castel (1688-1757) – French Jesuit physicist who worked on gravity and optics in a Cartesian context
- Benedetto Castelli (1578–1643) – Benedictine mathematician; long-time friend and supporter of Galileo Galilei, who was his teacher; wrote an important work on fluids in motion
- Bonaventura Cavalieri (1598–1647) – Jesuate (not to be confused with Jesuit) known for his work on the problems of optics and motion, work on the precursors of infinitesimal calculus, and the introduction of logarithms to Italy; his principle in geometry partially anticipated integral calculus; the lunar crater Cavalerius is named in his honor
- Antonio José Cavanilles (1745–1804) – priest and leading Spanish taxonomic botanist of the 18th century
- Francesco Cetti (1726–1778) – Jesuit zoologist and mathematician
- Tommaso Ceva (1648–1737) – Jesuit mathematician, poet, and professor who wrote treatises on geometry, gravity, and arithmetic
- Christopher Clavius (1538–1612) – German mathematician and astronomer, most noted in connection with the Gregorian calendar, his arithmetic books were used by many mathematicians including Leibniz and Descartes
- Guy Consolmagno (1952–) – Jesuit astronomer and planetary scientist, serving as Director of the Vatican Observatory
- Nicolaus Copernicus (1473–1543) – Renaissance astronomer and canon famous for his heliocentric cosmology that set in motion the Copernican Revolution
- Vincenzo Coronelli (1650–1718) – Franciscan cosmographer, cartographer, encyclopedist, and globe-maker
- Bonaventura Corti (1729-1813) – Italian biologist and physicist who made microscopic observations on Tremels, Rotifers and seaweeds
- George Coyne (1933–) – Jesuit astronomer and former director of the Vatican Observatory whose research interests have been in polarimetric studies of various subjects including Seyfert galaxies
- James Cullen (mathematician) (1867–1933) – Jesuit mathematician who published what is now known as Cullen numbers in number theory
- James Curley (astronomer) (1796–1889) – Jesuit, first director of Georgetown Observatory and determined the latitude and longitude of Washington, D.C.
- Albert Curtz (1600–1671) – Jesuit astronomer who expanded on the works of Tycho Brahe and contributed to early understanding of the moon; the crater Curtius on the Moon is named after him
- Johann Baptist Cysat (1587–1657) – Jesuit mathematician and astronomer, after whom the lunar crater Cysatus is named; published the first printed European book concerning Japan; one of the first to make use of the newly developed telescope; did important research on comets and the Orion nebula
- Jean-Baptiste Chappe d’Auteroche (1722–1769) – priest and astronomer best known for his observations of the transits of Venus
- Ignazio Danti (1536–1586) – Dominican mathematician, astronomer, cosmographer, and cartographer
- Armand David (1826–1900) – Lazarist priest, zoologist, and botanist who did important work in these fields in China
- Francesco Denza (1834–1894) – Barnabite meteorologist, astronomer, and director of Vatican Observatory
- Václav Prokop Diviš (1698–1765) – Czech priest who studied electrical phenomenons and constructed, among other inventions, the first electrified musical instrument in history
- Alberto Dou Mas de Xaxàs (1915–2009) – Spanish Jesuit priest who was president of the Royal Society of Mathematics, member of the Royal Academy of Natural, Physical, and Exact Sciences, and one of the foremost mathematicians of his country
- Johann Dzierzon (1811–1906) – priest and pioneering apiarist who discovered the phenomenon of parthenogenesis among bees, and designed the first successful movable-frame beehive; has been described as the „father of modern apiculture”
- Francesco Faà di Bruno (c. 1825–1888) – priest and mathematician beatified by Pope John Paul II
- Honoré Fabri (1607–1688) – Jesuit mathematician and physicist
- Jean-Charles de la Faille (1597–1652) – Jesuit mathematician who determined the center of gravity of the sector of a circle for the first time
- Gabriele Falloppio (1523–1562) – Canon and one of the most important anatomists and physicians of the sixteenth century; the Fallopian tubes, which extend from the uterus to the ovaries, are named for him
- Gyula Fényi (1845–1927) – Jesuit astronomer and director of the Haynald Observatory; noted for his observations of the sun; the crater Fényi on the Moon is named after him
- Louis Feuillée (1660–1732) – Minim explorer, astronomer, geographer, and botanist
- Kevin T. FitzGerald (1955-) – American molecular biologist and holds the Dr. David Lauler chair in Catholic Health Care Ethics at Georgetown University
- Placidus Fixlmillner (1721–1791) – Benedictine priest and one of the first astronomers to compute the orbit of Uranus
- Paolo Frisi (1728–1784) – priest, mathematician, and astronomer who did significant work in hydraulics
- José Gabriel Funes (1963– ) – Jesuit astronomer and former director of the Vatican Observatory
- Lorenzo Fazzini (1787–1837) – priest and physicist born in Vieste and working in Neaples
- Joseph Galien (1699 – c. 1762) – Dominican professor who wrote on aeronautics, hailstorms, and airships
- Jean Gallois (1632–1707) – French scholar, abbot, and member of Academie des sciences
- Pierre Gassendi (1592–1655) – French priest, astronomer, and mathematician who published the first data on the transit of Mercury; best known intellectual project attempted to reconcile Epicurean atomism with Christianity
- Antoine Gaubil (1689-1759) – French astronomer who was the director general of the College of Interpreters at the court of China between 1741 and 1759 and centralized information provided by the Jesuit observatories throughout the world
- Agostino Gemelli (1878–1959) – Franciscan physician and psychologist; founded Catholic University of the Sacred Heart in Milan
- Johannes von Gmunden (c. 1380–1442) – Canon, mathematician, and astronomer who compiled astronomical tables; Asteroid 15955 Johannesgmunden named in his honor
- Carlos de Sigüenza y Góngora (1645–1700) – priest, polymath, mathematician, astronomer, and cartographer; drew the first map of all of New Spain
- Andrew Gordon (Benedictine) (1712–1751) – Benedictine monk, physicist, and inventor who made the first electric motor
- Christoph Grienberger (1561–1636) – Jesuit astronomer after whom the crater Gruemberger on the Moon is named; verified Galileo’s discovery of Jupiter’s moons.
- Francesco Maria Grimaldi (1618–1663) – Jesuit who discovered the diffraction of light (indeed coined the term „diffraction”), investigated the free fall of objects, and built and used instruments to measure geological features on the moon
- Robert Grosseteste (c. 1175 – 1253) – bishop who was one of the most knowledgeable men of the Middle Ages; has been called „the first man ever to write down a complete set of steps for performing a scientific experiment”
- Paul Guldin (1577–1643) – Jesuit mathematician and astronomer who discovered the Guldinus theorem to determine the surface and the volume of a solid of revolution
- Bartolomeu de Gusmão (1685–1724) – Jesuit known for his early work on lighter-than-air airship design
- Johann Georg Hagen (1847–1930) – Jesuit director of the Georgetown and Vatican Observatories; the crater Hagen on the Moon is named after him
- Frank Haig (1928-) – American physics professor
- Nicholas Halma (1755–1828) – French abbot, mathematician, and translator
- Jean-Baptiste du Hamel (1624–1706) – French priest, natural philosopher, and secretary of the Academie Royale des Sciences
- René Just Haüy (1743–1822) – priest known as the father of crystallography
- Maximilian Hell (1720–1792) – Jesuit astronomer and director of the Vienna Observatory who wrote astronomy tables and observed the Transit of Venus; the crater Hell on the Moon is named after him
- Michał Heller (1936– ) – Polish priest, Templeton Prize winner, and prolific writer on numerous scientific topics
- Lorenz Hengler (1806–1858) – priest often credited as the inventor of the horizontal pendulum
- Hermann of Reichenau (1013–1054) – Benedictine historian, music theorist, astronomer, and mathematician
- Pierre Marie Heude (1836–1902) – Jesuit missionary and zoologist who studied the natural history of Eastern Asia
- Franz von Paula Hladnik (1773–1844) – priest and botanist who discovered several new kinds of plants, and certain genera have been named after him
- Giovanni Battista Hodierna (1597–1660) – priest and astronomer who catalogued nebulous objects and developed an early microscope
- Johann Baptiste Horvath (1732-1799) – Hungarian physicist who taught physics and philosophy at the University of Tyrnau, later of Buda, and wrote many Newtonian textbooks
- Victor-Alphonse Huard (1853–1929) – priest, naturalist, educator, writer, and promoter of the natural sciences
- Maximus von Imhof (1758–1817) – German Augustinian physicist and director of the Munich Academy of Sciences
- Giovanni Inghirami (1779–1851) – Italian Piarist astronomer who has a valley on the moon named after him as well as a crater
- François Jacquier (1711–1788) – Franciscan mathematician and physicist; at his death he was connected with nearly all the great scientific and literary societies of Europe
- Stanley Jaki (1924–2009) – Benedictine priest and prolific writer who wrote on the relationship between science and theology
- Ányos Jedlik (1800–1895) – Benedictine engineer, physicist, and inventor; considered by Hungarians and Slovaks to be the unsung father of the dynamo and electric motor
- Georg Joseph Kamel (1661–1706) – Jesuit missionary and botanist who established the first pharmacy in the Philippines; the genus Camellia is named for him
- Karl Kehrle (1898–1996) – Benedictine Monk of Buckfast Abbey, England; beekeeper; world authority on bee breeding, developer of the Buckfast bee
- Eusebio Kino (1645–1711) – Jesuit missionary, mathematician, astronomer and cartographer; drew maps based on his explorations first showing that California was not an island, as then believed; published an astronomical treatise in Mexico City of his observations of the Kirsch comet
- Otto Kippes (1905–1994) – priest acknowledged for his work in asteroid orbit calculations; the main belt asteroid 1780 Kippes was named in his honour
- Athanasius Kircher (1602–1680) – Jesuit who has been called the father of Egyptology and „Master of a hundred arts”; wrote an encyclopedia of China; one of the first people to observe microbes through a microscope; in his Scrutinium Pestis of 1658 he noted the presence of „little worms” or „animalcules” in the blood, and concluded that the disease was caused by micro-organisms; this is antecedent to germ theory
- Wenceslas Pantaleon Kirwitzer (1588–1626) – Jesuit astronomer and missionary to China who published observations of comets
- Jan Krzysztof Kluk (1739–1796) – priest, naturalist agronomist, and entomologist who wrote a multi-volume work on Polish animal life
- Marian Wolfgang Koller (1792–1866) – Benedictine professor who wrote on astronomy, physics, and meteorology
- Franz Xaver Kugler (1862–1929) – Jesuit chemist, mathematician, and Assyriologist who is most noted for his studies of cuneiform tablets and Babylonian astronomy
- Ramon Llull (ca. 1232 – ca. 1315) – Majorcan writer and philosopher, logician and a Franciscan tertiary considered a pioneer of computation theory
- Nicolas Louis de Lacaille (1713–1762) – French deacon and astronomer noted for cataloguing stars, nebulous objects, and constellations
- Eugene Lafont (1837–1908) – Jesuit physicist, astronomer, and founder of the first Scientific Society in India
- Antoine de Laloubère (1600–1664) – Jesuit and first mathematician to study the properties of the helix
- Bernard Lamy (1640–1715) – Oratorian philosopher and mathematician who wrote on the parallelogram of forces
- Pierre André Latreille (1762–1833) – priest and entomologist whose works describing insects assigned many of the insect taxa still in use today
- Georges Lemaître (1894–1966) – Belgian priest and father of the Big Bang theory
- Émile Licent (1876–1952) – French Jesuit trained as a natural historian; spent more than 25 years researching in Tianjin, China
- Joseph Xaver Liesganig (1719-1799) – Austrian astronomer and geodesist who managed the Jesuit observatory in Vienna between 1756 and 1773
- Thomas Linacre (c. 1460–1524) – English priest, humanist, translator, and physician
- Francis Line (1595–1675) – Jesuit magnetic clock and sundial maker who disagreed with some of the findings of Newton and Boyle
- Juan Caramuel y Lobkowitz (1606–1682) – Cistercian who wrote on a variety of scientific subjects, including probability theory
- João de Loureiro (1717–1791) – Portuguese mathematician and botanist active in Cochinchina
- Jean Mabillon (1632–1707) – Benedictine monk and scholar, considered the founder of palaeography and diplomatics
- James B. Macelwane (1883–1956) – Jesuit seismologist who contributed a volume to the first textbook on seismology in America
- John MacEnery (1797–1841) – archaeologist who investigated the Palaeolithic remains at Kents Cavern
- Manuel Magri (1851–1907) – Jesuit ethnographer, archaeologist and writer; one of Malta’s pioneers in archaeology
- Emmanuel Maignan (1601–1676) – Minim physicist and professor of medicine who published works on gnomonics and perspective
- Pal Mako (1724-1793) – Hungarian mathematician and physicist who taught mathematics, experimental physics and mechanics at the Vienna Theresianum and had a part in the preparation of the Ratio educationis (1777), which reformed the imperial teaching system in the spirit of Enlightenment
- Charles Malapert (1581–1630) – Jesuit writer, astronomer, and proponent of Aristotelian cosmology; also known for observations of sunpots, the lunar surface, and the southern sky; the crater Malapert on the Moon is named after him
- Nicolas Malebranche (1638–1715) – Oratorian philosopher who studied physics, optics, and the laws of motion and disseminated the ideas of Descartes and Leibniz
- Marcin of Urzędów (c. 1500–1573) – priest, physician, pharmacist, and botanist
- Joseph Maréchal (1878–1944) – Jesuit philosopher and psychologist
- Marie-Victorin (1885–1944) – Christian Brother and botanist best known as the father of the Jardin botanique de Montréal
- Edme Mariotte (c. 1620–1684) – priest and physicist who recognized Boyle’s Law and wrote about the nature of color
- Francesco Maurolico (1494–1575) – Benedictine who made contributions to the fields of geometry, optics, conics, mechanics, music, and astronomy, and gave the first known proof by mathematical induction
- Christian Mayer (astronomer) (1719–1783) – Jesuit astronomer most noted for pioneering the study of binary stars
- James Robert McConnell (1915–1999) – Irish theoretical physicist, pontifical academician, Monsignor
- Michael C. McFarland (1948-) – American computer scientist and president of the College of the Holy Cross in Worcester, Massachusetts
- Paul McNally (1890–1955) – Jesuit astronomer and director of Georgetown Observatory; the crater McNally on the Moon is named after him
- Gregor Mendel (1822–1884) – Augustinian monk and father of genetics
- Pietro Mengoli (1626–1686) – priest and mathematician who first posed the famous Basel Problem
- Giuseppe Mercalli (1850–1914) – priest, volcanologist, and director of the Vesuvius Observatory who is best remembered today for his Mercalli scale for measuring earthquakes which is still in use
- Marin Mersenne (1588–1648) – Minim philosopher, mathematician, and music theorist, so-called „father of acoustics”
- Paul of Middelburg (1446–1534) – Bishop who wrote on the reform of the calendar
- Maciej Miechowita (1457–1523) – Canon who wrote the first accurate geographical and ethnographical description of Eastern Europe, as well as two medical treatises
- François-Napoléon-Marie Moigno (1804–1884) – Jesuit physicist and mathematician; was an expositor of science and translator rather than an original investigator
- Juan Ignacio Molina (1740–1829) – Jesuit naturalist, historian, botanist, ornithologist and geographer
- Louis Moréri (1643–1680) – 17th-century priest and encyclopaedist
- Theodorus Moretus (1602–1667) – Jesuit mathematician and author of the first mathematical dissertations ever defended in Prague; the lunar crater Moretus is named after him
- Landell de Moura (1861–1928) – priest and inventor who was the first to accomplish the transmission of the human voice by a wireless machine
- Gabriel Mouton (1618–1694) – abbot, mathematician, astronomer, and early proponent of the metric system
- Jozef Murgaš (1864–1929) – priest who contributed to wireless telegraphy and helped develop mobile communications and wireless transmission of information and human voice
- José Celestino Mutis (1732–1808) – Canon, botanist, and mathematician who led the Royal Botanical Expedition of the New World
- Bienvenido Nebres (1940-) – Filipino mathematician, president of Ateneo de Manila University, and an honoree of the National Scientist of the Philippines award
- Jean François Niceron (1613–1646) – Minim mathematician who studied geometrical optics
- Nicholas of Cusa (1401–1464) – Cardinal, philosopher, jurist, mathematician, astronomer, and one of the great geniuses and polymaths of the 15th century
- Julius Nieuwland (1878–1936) – Holy Cross priest, known for his contributions to acetylene research and its use as the basis for one type of synthetic rubber, which eventually led to the invention of neoprene by DuPont
- Jean-Antoine Nollet (1700–1770) – abbot and physicist who discovered the phenomenon of osmosis in natural membranes
- Hugo Obermaier (1877–1946) – priest, prehistorian, and anthropologist who is known for his work on the diffusion of mankind in Europe during the Ice Age, as well as his work with north Spanish cave art
- William of Ockham (c. 1288 – c. 1348) – Franciscan Scholastic who wrote significant works on logic, physics, and theology; known for Occam’s razor-principle
- Nicole Oresme (c. 1323–1382) – one of the most famous and influential philosophers of the later Middle Ages; economist, mathematician, physicist, astronomer, philosopher, theologian and Bishop of Lisieux, and competent translator; one of the most original thinkers of the 14th century
- Barnaba Oriani (1752–1832) – Barnabite geodesist, astronomer and scientist whose greatest achievement was his detailed research of the planet Uranus; also known for Oriani’s theorem
- Tadeusz Pacholczyk (1965–) – priest, neuroscientist and writer
- Luca Pacioli (c. 1446–1517) – Franciscan friar who published several works on mathematics; often regarded as the „father of accounting”
- Ignace-Gaston Pardies (1636–1673) – Jesuit physicist known for his correspondence with Newton and Descartes
- Franciscus Patricius (1529–1597) – priest, cosmic theorist, philosopher, and Renaissance scholar
- John Peckham (1230–1292) – Archbishop of Canterbury and early practitioner of experimental science
- Nicolas Claude Fabri de Peiresc (1580–1637) – abbot and astromer who discovered the Orion Nebula; lunar crater Peirescius named in his honor
- Stephen Joseph Perry (1833–1889) – Jesuit astronomer and Fellow of the Royal Society; made frequent observations of Jupiter’s satellites, of stellar occultations, of comets, of meteorites, of sun spots, and faculae
- Giambattista Pianciani (1784–1862) – Jesuit mathematician and physicist who established the electric nature of aurora borealis
- Giuseppe Piazzi (1746–1826) – Theatine mathematician and astronomer who discovered Ceres, today known as the largest member of the asteroid belt; also did important work cataloguing stars
- Jean Picard (1620–1682) – priest and first person to measure the size of the Earth to a reasonable degree of accuracy; also developed what became the standard method for measuring the right ascension of a celestial object; the PICARD mission, an orbiting solar observatory, is named in his honor
- Edward Pigot (1858–1929) – Jesuit seismologist and astronomer
- Alexandre Guy Pingré (1711–1796) – French priest astronomer and naval geographer; the crater Pingré on the Moon is named after him, as is the asteroid 12719 Pingré
- Andrew Pinsent (1966–) – priest whose current research includes the application of insights from autism and social cognition to 'second-person' accounts of moral perception and character formation; his previous scientific research contributed to the DELPHI experiment at CERN
- Jean Baptiste François Pitra (1812–1889) – Benedictine cardinal, archaeologist and theologian who noteworthy for his great archaeological discoveries
- Charles Plumier (1646–1704) – Minim friar who is considered one of the most important botanical explorers of his time
- Marcin Odlanicki Poczobutt (1728–1810) – Jesuit astronomer and mathematician; granted the title of the King’s Astronomer; the crater Poczobutt on the Moon is named after him; taught astronomy at Vilna University (1764-1808), managed its observatory and was the rector of Vilna University between 1777 and 1808
- Léon Abel Provancher (1820–1892) – priest and naturalist devoted to the study and description of the fauna and flora of Canada; his pioneer work won for him the appellation of the „father of natural history in Canada”
- Claude Rabuel – mathematician
- Louis Receveur (1757–1788) – Franciscan naturalist and astronomer; described as being as close as one could get to being an ecologist in the 18th century
- Franz Reinzer (1661–1708) – Jesuit who wrote an in-depth meteorological, astrological, and political compendium covering topics such as comets, meteors, lightning, winds, fossils, metals, bodies of water, and subterranean treasures and secrets of the earth
- Louis Rendu (1789–1859) – bishop who wrote an important book on the mechanisms of glacial motion; the Rendu Glacier, Alaska, US and Mount Rendu, Antarctica are named for him
- Vincenzo Riccati (1707–1775) – Italian Jesuit mathematician and physicist
- Matteo Ricci (1552–1610) – one of the founding fathers of the Jesuit China Mission and co-author of the first European-Chinese dictionary
- Giovanni Battista Riccioli (1598–1671) – Jesuit astronomer who authored Almagestum novum, an influential encyclopedia of astronomy; the first person to measure the rate of acceleration of a freely falling body; created a selenograph with Father Grimaldi that now adorns the entrance at the National Air and Space Museum in Washington, D.C.; first to note that Mizar was a „double star„
- Richard of Wallingford (1292–1336) – abbot, renowned clockmaker, and one of the initiators of western trigonometry
- Lluis Rodés (1881-1939) – Spanish astronomer and director of Observatorio del Ebro, wrote El Frmamento
- Johannes Ruysch (c. 1460–1533) – priest, explorer, cartographer, and astronomer who created the second oldest known printed representation of the New World
- Giovanni Girolamo Saccheri (1667–1733) – Jesuit mathematician and geometer who was perhaps the first European to write about Non-Euclidean geometry
- Johannes de Sacrobosco (c. 1195 – c. 1256) – Irish monk and astronomer who wrote the authoritative medieval astronomy text Tractatus de Sphaera; his Algorismus was the first text to introduce Hindu-Arabic numerals and procedures into the European university curriculum; the lunar crater Sacrobosco is named after him
- Gregoire de Saint-Vincent (1584–1667) – Jesuit mathematician who made important contributions to the study of the hyperbola
- Alphonse Antonio de Sarasa (1618–1667) – Jesuit mathematician who contributed to the understanding of logarithms
- Christoph Scheiner (c. 1573–1650) – Jesuit physicist, astronomer, and inventor of the pantograph; wrote on a wide range of scientific subjects, including sunspots, leading to a dispute with Galileo Galilei
- Wilhelm Schmidt (linguist) (1868–1954) – Austrian priest, linguist, anthropologist, and ethnologist
- George Schoener (1864–1941) – priest who became known in the United States as the „Padre of the Roses” for his experiments in rose breeding
- Gaspar Schott (1608–1666) – Jesuit physicist, astronomer, and natural philosopher who is most widely known for his works on hydraulic and mechanical instruments
- Franz Paula von Schrank (1747–1835) – priest, botanist, entomologist, and prolific writer
- Berthold Schwarz (c. 14th century) – Franciscan friar and reputed inventor of gunpowder and firearms
- Anton Maria Schyrleus of Rheita (1604–1660) – Capuchin astronomer and optician who built Kepler’s telescope
- George Mary Searle (1839–1918) – Paulist astronomer and professor who discovered six galaxies
- Angelo Secchi (1818–1878) – Jesuit pioneer in astronomical spectroscopy and one of the first scientists to state authoritatively that the sun is a star; discovered the existence of solar spicules and drew an early map of Mars
- Alessandro Serpieri (1823–1885) – priest, astronomer, and seismologist who studied shooting stars, and was the first to introduce the concept of the seismic radiant
- Gerolamo Sersale (1584–1654) – Jesuit astronomer and selenographer; his map of the moon can be seen in the Naval Observatory of San Fernando; the lunar crater Sirsalis is named after him
- Benedict Sestini (1816–1890) – Jesuit astronomer, mathematician and architect; studied sunspots and eclipses; wrote textbooks on a variety of mathematical subjects
- René François Walter de Sluse (1622–1685) – Canon and mathematician with a family of curves named after him
- Domingo de Soto (1494–1560) – Spanish Dominican priest and professor at the University of Salamanca; in his commentaries to Aristotle he proposed that free falling bodies undergo constant acceleration
- Lazzaro Spallanzani (1729–1799) – priest, biologist, and physiologist who made important contributions to the experimental study of bodily functions, animal reproduction, and essentially discovered echolocation; his research of biogenesis paved the way for the investigations of Louis Pasteur
- Valentin Stansel (1621–1705) – Jesuit astronomer in Brazil, who discovered a comet, which, after accurate positions were made via F. de Gottignies in Goa, became known as the Estancel-Gottignies comet
- Johan Stein (1871–1951) – Jesuit astronomer and director of the Vatican Observatory, which he modernized and relocated to Castel Gandolfo; the crater Stein on the far side of the Moon is named after him
- Nicolas Steno (1638–1686) – Bishop beatified by Pope John Paul II who is often called the father of geology and stratigraphy, and is known for Steno’s principles
- Joseph Stepling (1716-1778) – Bohemian astronomer, physicist and mathematician who managed the Jesuit observatory in Prague between 1751 and 1778
- Pope Sylvester II (c. 946–1003) – Prolific scholar who endorsed and promoted Arabic knowledge of arithmetic, mathematics, and astronomy in Europe, reintroducing the abacus and armillary sphere which had been lost to Europe since the end of the Greco-Roman era
- Alexius Sylvius Polonus (1593 – c. 1653) – Jesuit astronomer who studied sunspots and published a work on calendariography
- Ignacije Szentmartony (1718–1793) – Jesuit cartographer and royal mathematician and astronomer, who became a member of the expedition that worked on the rearrangement of the frontiers among colonies in South America, especially Brazil
- André Tacquet (1612–1660) – Jesuit mathematician whose work laid the groundwork for the eventual discovery of calculus
- Pierre Teilhard de Chardin (1881–1955) – Jesuit paleontologist and geologist who took part in the discovery of Peking Man
- Francesco Lana de Terzi (c. 1631–1687) – Jesuit referred to as the Father of Aviation for his pioneering efforts; he also developed a blind writing alphabet prior to Braille.
- Theodoric of Freiberg (c. 1250 – c. 1310) – Dominican theologian and physicist who gave the first correct geometrical analysis of the rainbow
- Joseph Tiefenthaler (1710–1785) – Jesuit who was one of the earliest European geographers to write about India
- Giuseppe Toaldo (1719–1797) – priest and physicist who studied atmospheric electricity and did important work with lightning rods; the asteroid 23685 Toaldo is named for him
- José Torrubia (c. 1700–1768) – Franciscan linguist, scientist, collector of fossils and books, and writer on historical, political and religious subjects
- Franz de Paula Triesnecker (1745–1817) – Jesuit astronomer and director of the Vienna Observatory; published a number of treatises on astronomy and geography; the crater Triesnecker on the Moon is named after him
- Luca Valerio (1552–1618) – Jesuit mathematician who developed ways to find volumes and centers of gravity of solid bodies
- Pierre Varignon (1654–1722) – priest and mathematician whose principle contributions were to statics and mechanics; created a mechanical explanation of gravitation
- Jacques de Vaucanson (1709–1782) – French Minim friar inventor and artist who was responsible for the creation of impressive and innovative automata and machines such as the first completely automated loom
- Giovanni Battista Venturi (1746–1822) – priest who discovered the Venturi effect
- Fausto Veranzio (c. 1551–1617) – Bishop, polymath, inventor, and lexicographer
- Ferdinand Verbiest (1623–1688) – Jesuit astronomer and mathematician; designed what some claim to be the first ever self-propelled vehicle, which many claim this as the world’s first automobile
- Francesco de Vico (1805–1848) – Jesuit astronomer who discovered or co-discovered a number of comets; also made observations of Saturn and the gaps in its rings; the lunar crater De Vico and the asteroid 20103 de Vico are named after him
- Vincent of Beauvais (c.1190–c.1264) – Dominican who wrote the most influential encyclopedia of the Middle Ages
- Benito Vines (1837–1893) – Jesuit meteorologist known as „Father Hurricane” who made the first weather model to predict the trajectory of a hurricane
- János Vitéz (archbishop) (c.1405–1472) – Archbishop, astronomer, and mathematician
- Martin Waldseemüller (c. 1470–1520) – German priest and cartographer who, along with Matthias Ringmann, is credited with the first recorded usage of the word America
- Erich Wasmann (1859–1931) – Austrian entomologist known for Wasmannian mimicry
- Godefroy Wendelin (1580–1667) – priest and astronomer who recognized that Kepler’s third law applied to the satellites of Jupiter; the lunar crater Vendelinus is named in his honor
- Johannes Werner (1468–1522) – priest, mathematician, astronomer, and geographer
- Witelo (c. 1230 – after 1280, before 1314) – Friar, physicist, natural philosopher, and mathematician; lunar crater Vitello named in his honor; his Perspectiva powerfully influenced later scientists, in particular Johannes Kepler
- Julian Tenison Woods (1832–1889) – Passionist geologist and mineralogist
- Theodor Wulf (1868–1946) – Jesuit physicist who was one of the first experimenters to detect excess atmospheric radiation
- Franz Xaver von Wulfen (1728–1805) – Jesuit botanist, mineralogist, and alpinist
- Leonardo Ximenes (1711-1786) – Italian physicist and astronomer, specialist of hydraulics, creator and director of the Observatory San Giovanino in Florence
- John Zahm (1851–1921) – Holy Cross priest and South American explorer
- Giuseppe Zamboni (1776–1846) – priest and physicist who invented the Zamboni pile, an early electric battery similar to the Voltaic pile
- Francesco Zantedeschi (1797–1873) – priest who was among the first to recognize the marked absorption by the atmosphere of red, yellow, and green light; published papers on the production of electric currents in closed circuits by the approach and withdrawal of a magnet, thereby anticipating Michael Faraday’s classical experiments of 1831
- Niccolò Zucchi (1586–1670) – claimed to have tried to build a reflecting telescope in 1616 but abandoned the idea (maybe due to the poor quality of the mirror); may have been the first to see the belts on the planet Jupiter (1630)
- Giovanni Battista Zupi (c. 1590–1650) – Jesuit astronomer, mathematician, and first person to discover that the planet Mercury had orbital phases; the crater Zupus on the Moon is named after him