He was appointed a Knight of the Thistle in 1761 and was a Scottish representative peer from 1761. He was Vice Admiral of Scotland from 1767 to 1776. He was Lord Lieutenant of Dumfries from 1794 until 1810.
He succeeded his father in the Earldom of March in 1731 and his mother in the Earldom of Ruglen in 1748.
Queensberry never married, though he had a daughter, Maria "Mie-Mie" Fagnani, by a mistress, the Marchesa Fagnani. In 1798, she became the wife of the 3rd Marquess of Hertford.
Queensberry left much of his fortune to Maria Hertford. The Earldom of Ruglen became extinct.
He left £10,000 to Lady Anne Hamilton who was a Lady in Waiting to Caroline of Brunswick.
As Lord March he is portrayed in the William Makepeace Thackeray novel The Virginians as a dissolute gambler.