Stuart's talents were first displayed in his judicious corrections and amendments to the ‘Gospel History’ (1765) of the Rev. Robert Wait. His first independent work was the anonymous ‘Historical Dissertation on the Antiquity of the English Constitution,’ published in the spring of 1768, in which he traced English institutions to a German source. The second edition, which came out in January 1770, with a dedication to Lord Mansfield, bore Stuart's name on the title-page, and it was republished in 1778 and 1790. For this work he received from Edinburgh University on 16 Nov. 1769 the degree of doctor of law (Cat. of Graduates, 1858, p. 257).
Later in 1768 Stuart proceeded to London, putting his hope of preferment in the patronage of Lord Mansfield, but his expectations were disappointed. In 1769 he lodged with Thomas Somerville [q. v.] in the house of Murdoch the bookseller, where he was every day engaged on articles for the newspapers and reviews. Stuart was already conspicuous among the writers in the ‘Monthly Review,’ for which he worked from 1768 to 1773. Somerville was surprised by his lack of principle—he would boast that he had written two articles on the same public character, ‘one a panegyric and the other a libel,’ for each of which he would receive a guinea—and by his amazing rapidity of composition. After a night's revel he would, without any sleep, compose in a few minutes an article which was sent to the press without correction (Somerville, Life and Times, pp. 148–50, 275–6). While residing in London he supervised the manuscripts of Nathaniel Hooke (d. 1763) [q. v.], and from them finished the fourth volume of Hooke's ‘Roman History,’ which was published in 1771.
By June 1773 Stuart was back with his father at Musselburgh, and was busy over the arrangements for the issue of the ‘Edinburgh Magazine and Review,’ which was ‘to be formed and conducted by him,’ and for which he engaged ‘to furnish the press with copy.’ The first number—that for November 1773—came out about the middle of October in that year, and it was discontinued after the publication of the number for August 1776, when five octavo volumes had been completed. The chief writers in it, in addition to Stuart, were Professor Richardson of Glasgow, Professor William Baron, Thomas Blacklock, Rev. A. Gillies, and William Smellie, the Scottish printer, and it was conducted for some time ‘with great spirit, much display of talent, and conspicuous merit.’ These advantages were soon rendered nugatory by the malevolence of Stuart, ‘a disappointed man, thwarted in his early prospects of establishment in life.’ The fame of the other historians and of the leading writers at Edinburgh diseased his mind, and Smellie's energies were constantly employed in checkmating his virulence. He wished to ornament the first number of the magazine ‘with a print of my Lord Monboddo in his quadruped form,’ but his purpose was frustrated. His slashing article on the ‘Elements of Criticism,’ the work of Lord Kames, was completely metamorphosed by Smellie into a panegyric. In some matters, however, he had his own way. When David Hume reviewed the second volume of Dr. Henry's ‘History of Great Britain’ in very laudatory language, the article was cancelled and one by Stuart substituted for it, which erred in the other extreme (Smellie, David Hume, pp. 203–4; Burton, David Hume, ii. 415–16, 468–70). The climax was reached in an article by him and Gillies, written in spite of the remonstrances of Smellie, ‘with shocking scurrility and abuse,’ on Lord Monboddo's ‘Origin and Progress of Language,’ which ran through several numbers of the fifth volume, and the magazine was stopped (a list of his reviews and essays is given in Kerr, Life of Smellie, i. 403–8).
After this Stuart temporarily abandoned review-writing for the study of philosophy and history. He appended in 1776 to the second edition of Francis Stoughton Sullivan's ‘Lectures on the Constitution and Laws of England’ the authorities for the statements and a discourse on the government and laws of our country, and dedicated the volume to Lord North; the whole work was reissued at Portland, Maine, in 1805. His most important treatise, ‘A View of Society in Europe,’ was published in 1778, and reprinted in 1782, 1783, 1792, and 1813, and a French translation by A. H. M. Boulard, came out in Paris in 1789, in two volumes. Letters from Blackstone and Dr. Alexander Garden were added to the posthumous edition of 1792 by Stuart's father. In this dissertation the author followed the guidance of Montesquieu, whom alone, such was his vanity, he recognised as a superior. It was confined to the early and mediæval ages, and its learning was not sufficiently deep to give it permanent authority.
About 1779 Stuart was an unsuccessful candidate for the professorship of public law in the university of Edinburgh, and he believed that his failure was due to the influence of Robertson (Encyclop. Brit. 7th ed. xx. 780–4). From this time he pursued that
