From The Cabinet of Irish Literature, Volume 1 (1880), edited by Charles A. Read
Thomas Leland was born in Dublin in the year 1722, and was educated at the school or Dr. Sheridan, grandfather of the famous Richard Brinsley Sheridan. At the age of fifteen he entered Trinity College, and in his nineteenth year obtained a scholarship. In 1745 he was unsuccessful in an attempt to procure a fellowship, but next year gained it easily. In 1748 he entered into holy orders, and the same year published the result of his anxious meditation on the duties of the ministry, under the title of The Helps and Impediments to the Acquisition of Knowledge in Religious and Moral Subjects. This essay was much admired on its appearance, but it is believed to be not now extant.
Some time after this he was requested by the university to produce a new edition of Demosthenes, and in 1754 the first volume of his celebrated translation appeared. This was completed in two more volumes, the last of which was issued in 1770. This translation, together with the critical notes which accompanied it, at once established his reputation in England as a scholar. It was therefore with warm anticipations of success that his Life and Reign of Philip King of Macedon was received in 1758. These were not doomed to disappointment, for the work was at once successful, and continues to this day the best on the subject. In 1763 he was appointed professor of oratory in Trinity College, and soon after published The Principles of Human Eloquence, which was fiercely attacked by Warburton and Hurd. To them he replied with great force, obtaining a complete victory over both, as the best critics acknowledge.
After this, Leland turned his attention to the study of Irish history, and in a comparatively short time produced his History of Ireland, a work which is written in the best historical manner and graced with a pure style. This work, though highly successful from a critical point of view, was too impartial to be accepted by either of the two parties into which Ireland was then divided, and the author had consequently to be content with its praise and purchase by men of sense, a limited class in any nation. However, as years passed on the work grew in favour even with partisans, and to-day no library devoted to Irish matters is complete without it. The work had also a fair success in England, where party spirit did not run so high.
By this time Leland had not only established his position as a writer, but also as an eloquent preacher, and when Viscount Townshend became lord-lieutenant, in October, 1767, it was expected that he would be rewarded with some rich preferment. Preferment did indeed come to him, but not such as his friends expected. Early in 1768 he was appointed to the vicarage of Bray together with the prebend of Rathmichael, and soon after settled down to parochial work. After passing a quiet evening of life he died in the year 1785.
Dr. Johnson had a high opinion of Leland's works, as may be seen in several places in Boswell's Life. Dr. Parr had also a high regard for him, and says, "Of Leland my opinion is not founded on hearsay evidence, nor is it determined solely by the great authority of Dr. Johnson. ... I may with confidence appeal to writings which have long contributed to public amusement, and have often been honoured by public approbation; to the life of Philip, to the translation of Demosthenes, to the judicious dissertation upon eloquence, and to the spirited defence of that dissertation."