He was wounded in 1780 at the Battle of Martinique, and retired from the service in 1783; after living in financial difficulties for some years, he published two moderately successful novels in the 1780s, the second of which drew extensively on his experiences as a half-pay officer.
He became the founder and sole editor of two pro-government daily newspapers, the Sun and the True Briton, which ran for over a decade, and eventually retired from journalistic work in 1806.
[9] He was hired as one of a number of journalists who wrote pamphlets and newspaper articles in support of the government during the winter of 1788–89, when George III's insanity had become a matter of very contentious debate.
This was secretly funded by members of the government, on a private basis; Heriot launched it on 1 October 1792,[13] and it quickly rose to become the second most popular newspaper in the country, behind The Times.
[14] He then launched the True Briton, a morning daily, on 1 January 1793;[15] it, too, was funded by the Treasury and maintained a strongly pro-government pro-Tory line.
[18] He continued to write during this period, including a history of Gibraltar (1792) to accompany a work by the artist Antonio de Poggi, and an account of the Battle of the Nile (1798).
[20] He left newspaper work in 1806 and became a commissioner for the lottery; in 1810 he was made an Army deputy paymaster-general in the West Indies; and in 1816 the comptroller of Chelsea Hospital.