He was the son of William Douglas, 7th Earl of Morton and Lady Anne Keith, daughter of George Keith, 5th Earl Marischal.
After his father's death, Robert acted in a high-handed way in Orkney, overriding udal law, to raise money for the royalist cause.
[1][2] At this point of the War of the Three Kingdoms the Morton control of Orkney assumed importance, because the forces of James Graham, 1st Marquess of Montrose intended in 1649 to land there and re-open the fighting in Scotland.
[4] He was succeeded by his son, William Douglas, 9th Earl of Morton.
He also had two daughters by his wife: Lady Anne Douglas, who married the Earl Marischal, and Lady Mary Douglas, who married Sir Donald Macdonald.