James was a younger brother of Robert Stewart, 1st Lord Lorne (1382–1449), whose descendants bore this title.
The Stewarts of Lorne were amongst his most trusted supporters, and their power greatly increased while the Douglas family controlled Scotland and the king was a mere 7 years of age.
However, the unexpected death of the 5th Earl of Douglas from a fever in 1439 saw power now being uneasily shared between William, 1st Lord Crichton, Chancellor of Scotland and Sir Alexander Livingston, Governor of Stirling Castle.
Stewart and his Douglas allies planned to remove the young James II, who was being held by Livingston in his stronghold of Stirling Castle.
She was a daughter of John Beaufort, 1st Earl of Somerset (son of Katherine Swynford and John of Gaunt, and a grandson of Edward III of England) by his wife Lady Margaret Holland, daughter of Thomas Holland, 2nd Earl of Kent and Alice FitzAlan.