3rd Duke of Queensberry. Son of James Douglas, 2nd Duke of Queensberry and Mary Boyle. One of his cousins were William Douglas. In 1720 he married Catherine Hyde, with whom he had two children, Henry Douglas (1722-1754) and Charles Douglas (1726-1756). Named Privy Councillor and Keeper of the Great Seal of Scotland by George III. Succeeded as Duke of Queensberry by William Douglas, Lord March.
Boswell contacted the Duke in 1762-63, asking him to advance his case for a position in the guard. On December 26, 1762, the Duke wrote to him, suggesting that he got himself a non-military career.