Thomas Hearne or Hearn (July 1678 – 10 June 1735) was an English diarist and prolific antiquary, particularly remembered for his published editions of many medieval English chronicles and other important historical texts.
Hearne was born at Littlefield Green in the parish of White Waltham, Berkshire, the son of George Hearn, the parish clerk. Having received his early education from his father, he showed such taste for study that a wealthy neighbour, Francis Cherry of Shottesbrooke (c. 1665–1713), a celebrated nonjuror, interested himself in the boy, and sent him to the school at Bray "on purpose to learn the Latin tongue". Soon Cherry took him into his own house, and his education was continued at Bray until Easter 1696, when he matriculated at St Edmund Hall, Oxford.
At the university he attracted the attention of Dr John Mill (1645–1707), the principal of St Edmund Hall, who employed him to compare manuscripts and in other ways. Having taken the degree of B.A. in 1699 he was made assistant keeper of the Bodleian Library, where he worked on the catalogue of books, and in 1712 he was appointed second keeper. In 1715 Hearne was elected Architypographus and Esquire Bedell in civil law in the university, but objection having been made to his holding this office together with that of second librarian, he resigned it in the same year.
A nonjuror himself, he refused to take the oaths of allegiance to King George I, and early in 1716 he was deprived of his librarianship, and "he was, in fact, locked out of the library.". However, he continued to reside in Oxford, and occupied himself in editing the English chroniclers. Hearne refused several important academic positions, including the librarianship of the Bodleian and the Camden professorship of ancient history, rather than take the oaths. He died on 10 June 1735.