James Douglas, 3rd Earl of Morton (died 1548[1]) was a son of John Douglas, 2nd Earl of Morton and a grandson of James Douglas, 1st Earl of Morton and Joan of Scotland, a daughter of James I of Scotland. He married Catherine Stewart, an illegitimate daughter of King James IV of Scotland by his mistress Marion Boyd. The couple had three daughters; Margaret, Beatrix, and Elizabeth. He was succeeded by his son-in-law, James Douglas, 4th Earl of Morton, husband of his daughter Elizabeth.
His daughter Lady Margaret Douglas married James Hamilton, 2nd Earl of Arran, who was heir presumptive to Mary, Queen of Scots, prior to the birth of her son James in 1566. Beatrix married Robert Maxwell, 6th Lord Maxwell. Morton's three daughters were all affected by mental ill-health.[2]