The second son of James, 6th Duke of Hamilton and 3rd Duke of Brandon [d. 1758], and his wife Elizabeth (created Baroness Hamilton in 1776), Douglas Hamilton succeeded his elder brother, James George (7th Duke) in 1769. A Knight of the Order of the Thistle, on 5 April 1778 he married Elizabeth Anne Burrell [d. 1837] (who, after the Duke's death, married the 1st Marquess of Exeter). They had no children; thus Sir Douglas was succeeded in the duchies by his uncle, Archibald Hamilton.