Archibald James Edward Douglas [formerly Stewart], first Baron Douglas (1748–1827), litigant and politician, the son of Sir John Stewart of Grandtully, third baronet (1687–1764), and his wife, Lady Jane Douglas (1698–1753), was born on 10 July 1748 at Faubourg St Germain, Paris.

His early life was dominated by the efforts of his parents and supporters to establish his identity as nephew and heir of Archibald Douglas, duke of Douglas (bap. 1694, d. 1761). His mother, the duke's only sister, had in 1746 married without her brother's knowledge Colonel John Stewart, a former Jacobite sympathizer and veteran of the Swedish army, and fled to the continent. Two years later she informed the duke of the marriage and notified him that she was (at the age of fifty) pregnant. Subsequently she reported the birth on 10 July 1748 of twin boys, named Archibald and Sholto(1). The irascible and eccentric duke disapproved of the marriage, cut off his sister's allowance, and—encouraged by the duke of Hamilton's family, who stood next in line to the sister as heir—refused to recognize the twins as hers. In 1751 the family returned to Britain, where they lived a hand-to-mouth existence as Colonel Stewart was soon imprisoned for debt.

Sholto and Lady Jane both died in 1753.

Archibald's upbringing was taken over by Lady Schaw of Greenock, and, after her death in 1757, by the duke and duchess of Queensberry, who saw to his education, first at Rugby School (1759–61) and then at Westminster School (1761–5). The reclusive duke of Douglas surprisingly married in March 1758, and the new duchess, Margaret Douglas of Mains, became an aggressive advocate of Archibald's claim to the Douglas estates, which were said to be worth in excess of £12,000 a year. Before the duke died, she convinced him to reinvestigate the case and to name Archibald as his heir. Following the duke's death in July 1761, Archibald Stewart was duly served heir and took the surname Douglas.

This set the stage for one of the eighteenth century's most famous legal battles, the Douglas cause. Archibald's inheritance was challenged by the Hamiltons, who argued that he and his brother were supposititious. The Hamilton lawyers put together a plausible circumstantial argument that Archibald was actually Jacques Louis Mignon, the son of a Parisian glassworker, who had disappeared in July 1748. The case was litigated at great length and expense (the two sides spent £54,000 between them). It attracted tremendous interest, especially in Scotland. Not only was a large estate at stake, but many felt that requiring Archibald Douglas to in effect prove his identity raised a question that could endanger the security of inheritance in general. In Scotland the Douglas side enjoyed broad popular support, with James Boswell an especially eager partisan, though many of the literati favoured the Hamilton side. In 1767 the court of session decided by the casting vote of the lord president against Douglas. Douglas appealed to the House of Lords which, following the opinions of law lords Mansfield and Camden, reversed the decision without a division.

Douglas settled easily into the life of a landed magnate. He was an improving landlord who continued the rebuilding of Douglas Castle begun by his uncle, though investment in the Ayr bank of Douglas, Heron & Co., which failed in 1772, complicated his finances during the 1770s. He also achieved a degree of political prominence as he worked to resurrect the Douglas interest in Lanarkshire, Berwickshire, Forfarshire, and elsewhere. He was elected member for Forfarshire in 1782, and was made lord lieutenant of the county in 1794. During the following year he raised a regiment of fencibles(2). In parliament he was a loyal, if silent, follower of Henry Dundas and William Pitt, a status that facilitated his successful pursuit of a peerage. Although he would have preferred an earldom, he was created Baron Douglas of Douglas in 1790.

Douglas married twice into ducal families: first, on 13 June 1771, Lady Lucie Graham (1751–1780), daughter of the second duke of Montrose, and second, on 13 May 1783, Lady Frances Scott (1750–1817), sister of the third duke of Buccleuch; among the children born of this second marriage was Caroline Lucy Scott, novelist. Horace Walpole commented that ‘it is proof of his sense, that he can forgive her person in favour of her merit’ (to Lady Ossory, 17 April 1783, Walpole, Corr., 33.399).

He was also the father of George Douglas (1788-1838), Captain in the Royal Navy

Douglas died on 26 December 1827 at Bothwell Castle, Lanarkshire. He was buried in Douglas parish church in the same county. Forever identified with the Douglas cause, as an adult he proved a rather unexceptional aristocrat.