Described as an "imbecile", and violently insane, he was kept under lock and key from childhood at Queensberry House in Edinburgh, now part of the Scottish Parliament complex. When the Act of Union was signed in 1707, the disruption from either the festivities or the riots resulted in his escape. Drumlanrig, then around ten years old, slaughtered a young scullion in the Holyrood kitchen, roasted him on a spit, and began to eat him before he was discovered and apprehended. He was afterwards known as 'The Cannibalistic Idiot', and the oven he used can still be seen in the Parliament's Allowances Office.
A novodamus (i.e., de novo damus, "we grant anew"; a charter containing a clause by which a feudal superior re-bestows a former grant under a new set of conditions) had been made out for his father's titles, excepting the marquessate of Queensberry in 1706, to remove James Douglas from the succession. He died in 1715 and was buried on February 17 1715 in Calverley churchyard. His brother Charles Douglas, 3rd Duke of Queensberry succeeded him.