O'Brien, Matthew (1814–55), mathematician, was born at Ennis, Co. Clare, the son of Matthew O'Brien, a doctor. Educated initially by a private tutor, he entered Trinity College, Dublin, in July 1830 at the age of sixteen, but in November 1834 transferred to Gonville and Caius College, Cambridge, where he was a scholar from 1835 to 1837. Graduating with a first-class in mathematics in 1838, he was ranked third in order of merit (third wrangler), a substantial achievement. He graduated MA three years later in 1841.
Before finishing his postgraduate degree, O'Brien became a junior fellow of Caius College (1840), but resigned within a year. In 1843–4 he acted as moderator for the mathematical degree, then in March 1844 he took up a position as professor of natural philosophy (a forerunner of physics) and astronomy in King's College, London, on the resignation of the Rev. Henry Moseley (1801–72). In 1849 he was appointed to a more lucrative position as lecturer in practical astronomy at the Royal Military Academy, Woolwich. When he was eventually appointed to the professorship at the Military Academy in 1854, he resigned as professor at King's College in favour of the better pay in the latter institution.
Though he is not one of the more famous Irish expatriates, he was one of several nineteenth-century Irish mathematicians, along with Robert Murphy (qv), Sir George Gabriel Stokes (qv), and William Thompson (qv), who made their name in England. He was a regular contributor to the mathematical journals of the day and to the King's College [Literary and Scientific] Magazine, an irregular publication printed between 1842 and 1850, in which he published various essays on topical mathematical questions related to astronomy. Together with other members of King's College staff, and under the leadership of Professor Frederick Denison Maurice, he took part in several extracurricular educational endeavours. One of the most notable of these (as part of the committee of education appointed to plan the curriculum for the new Queen's College, London, opened in May 1848) was the first higher education college for women, where he lectured in mathematics and science.
During his career O'Brien published several elementary textbooks on mathematics and astronomy as well as papers in Cambridge journals. Among his surviving works in the British Library are Mathematical tracts, part 1 (1840), of which no further parts were published; An elementary treatise on differential calculus (1842), which made extensive use of the method of limits; Plane co-ordinate geometry, part 1 (1844); ‘On a new notation for expressing various conditions and equations in geometry, mechanics, and astronomy’, published in the Transactions of the Cambridge Philosophical Society (1847); Lectures on natural philosophy (1849), based on his lectures at King's College; and A treatise on mathematical geography (1852), which formed part 1 of A manual of geographical science: mathematical, physical, historical and descriptive, edited by C. G. Nicolay and published between 1852 and 1859.
There is a dearth of information on O'Brien's personal life. He was an ordained clergyman in the Church of England, and had at least one child, Arthur Evanson O'Brien (b. 25 January 1849 at Norwood, Middlesex), who followed in his father's footsteps in obtaining a degree at Cambridge (1871) and being ordained a priest (1873). Matthew O'Brien died at Petit Ménage, on the island of Jersey, on 22 August 1855.