He was Lord High Treasurer of Scotland, and a zealous Royalist, who, on the outbreak of the Great Rebellion in 1642, provided £100,000 for the cause by selling his Dalkeith estates to the Earl of Buccleuch. He also expanded his other seat, Aberdour Castle in Fife, with a Renaissance-style east wing. Lady Margaret Douglas (1610–1678), married the 1st Marquess of Argyll and had issue.
Lady Anne Douglas (d 1667), married the 2nd Earl of Kinnoull and had issue.
Robert Douglas, 8th Earl of Morton (d 1649)
Lady Mary Douglas, married the 2nd Earl of Dunfermline and had issue. James Douglas, 10th Earl of Morton (d 1686)
Lady Isabel Douglas (d 1650), married the 2nd Marquess of Montrose and had issue.