Born in Peebles, Queensberry was the only son of William Douglas, 2nd Earl of March, and his wife, Lady Anne Hamilton.

A friend of the Prince of Wales, Douglas was appointed Gentleman of the Bedchamber to George III in 1760.

[2] He was appointed a Knight of the Thistle in 1761 and was one of the 16 Scottish representative peers for an elected term or possibly more from 1761, and was Vice Admiral of Scotland from 1767 to 1776.

However, due to behavior during the king's unusual, long-lasting, mental health latter-life illness he was deprived of his office as Gentleman of the Bedchamber in 1789, and for a while took refuge abroad.

[8] On death, the Dukedom and Drumlanrig Castle passed to his second cousin once removed, the third Duke of Buccleuch.

[1] As "Lord March", he is briefly portrayed or described in the William Makepeace Thackeray novel The Virginians as a dissolute gambler.