Born Archibald James Edward Stewart. Son of Sir John Stewart and Lady Jane Douglas, daughter of James, 2nd Marquis of Douglas. 1st Baron Douglas of Douglas (cr. 1790). Married firstly (1771) to Lady Lucy Graham (1751-1780) and secondly (1783) to Lady Frances Scott (1750-1817). He had 9 children (5 boys, 4 girls, most of whom reached old age).
In 1767 he lost a much-publicised court case concerning the rights to the extensive Douglas estates. His opponent, the Duke of Hamilton, claimed that Stewart was not the son of Lady Jane Douglas, and thus was not the rightful heir. In February 1769 the House of Lords reversed the decision.
He received his pre-university education at Westminster School in the early 1760s; philosopher Jeremy Bentham was also born in 1748 and attended the school at the same time. Douglas later became MP for Forfarshire (1782-1790) and Lord Lieutenant for Forfarshire (1794-1827).
The first mention of Douglas in Boswell's journals is in Boswell's London Journal on November 30, 1762, when Boswell had lunch with then schoolboys Douglas of Douglas and George Douglas, both of whom attended Westminster School.
Boswell later took a great interest in the court battle known as the "Douglas Cause" which Douglas finally won in 1769, making him the legal heir to the Douglas estates.
The "Douglas Cause" received so widespread public attention at the time, that transcripts, depositions and other material relating in some way or another to the case were published. Some of this material is available via AbeBooks under names such as "The Douglas Cause, Case of the Respondents, The Duke of Hamilton and Brandon, Marquis of Douglas Etc., Lord Douglas Hamilton, and Their Guardians, Sir Hew Dalrymple, Etc." and "Memorial for George-James Duke of Hamilton. Against the Person Pretending to be Archibald Stewart". Searching for keywords "douglas cause" and the years 1767, 1768 and 1769 should yield some results.
Boswell himself wrote the novel "Dorando, a Spanish Tale", which was a thinly disguised defence for Stewart's case.