[1] Although details of his origins in Scotland are unclear, he accompanied James I to England in 1603 and in 1609 was deputed to escort 800 troublesome followers of the fugitive Hugh O'Neill, 2nd Earl of Tyrone to Sweden.
After the outbreak of the Irish Rebellion of 1641 he was commissioned by Charles I to raise a regiment in Ireland, with which he managed to relieve Captain Audley Mervyn at Augher.
They were unsuccessful in preventing Sir Phelim O'Neill from capturing Strabane but managed to secure the Barony of Raphoe which helped to guarantee the safety of Londonderry.
Lack of support from England or Dublin meant that Stewart was forced to exhaust his own resources, and in the following spring his men were reduced to great extremities.
After the collapse of the Royalist cause in Ireland Stewart returned to Scotland but at the Restoration was given a company of foot and reappointed Governor of Londonderry as a reward for his services.