He was born at Raggal, Banffshire, where his father was a farmer, and educated at Aberdeen University. Through the influence of Dr Archibald Pitcairne he became an assistant in the Advocates' Library, Edinburgh. His chief writings at this period were editions of Florence Wilson's De Animi Tranquillitate Dialogus (1707), and the Cantici Solomonis Paraphrasis Poetica (1709) of Arthur Johnston (1587-1641), editor of the Deliciae Poetarum Scotorum. On the death of Dr Pitcairne he edited his friend's Latin verses, and arranged for the sale of his valuable library to Peter the Great of Russia.
In 1714 he published Rudiments of the Latin Tongue, which was long used in Scottish schools. In 1715 he edited, with notes and annotations, the works of George Buchanan in two volumes folio. As Ruddiman was a Jacobite, Buchanan's liberal views invited his criticism. A society of scholars was formed in Edinburgh to "vindicate that incomparably learned and pious author from the calumnies of Mr Thomas Ruddiman"; but Ruddiman's remains the standard edition, though George Logan, John Love, John Man and others attacked him with great vehemence. He founded (1715) a successful printing business, and in 1728 was appointed printer to the university. He acquired the Caledonian Mercury in 1729, and in 1730 was appointed keeper of the Advocates' Library, resigning in 1752.
Besides the works mentioned, the following writings of Ruddiman deserve notice: An edition of Gavin Douglas's Aeneid of Virgil (1710); the editing and completion of James Anderson's Selectus Diplomatum et Numismatum Scotiae Thesaurus (1739); Catalogue of the Advocates' Library (1733-42); and a famous edition of Livy (1751). He also helped Joseph Ames with the Typographical Antiquities. Ruddiman was for many years the representative scholar of Scotland. Writing in 1766, Dr Johnson, after reproving James Boswell for some bad Latin, significantly adds--"Ruddiman is dead." When Boswell proposed to write Ruddiman's life, “ I should take pleasure in helping you to do honour to him,” said Johnson.
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