Born the second son of John Stewart MP (died 1769) of Castle Stewart, and brother of William Stewart MP,[2] Stewart was commissioned as an ensign in the 37th Regiment of Foot on 8 April 1755.[3] He commanded a field force at Orangeburg and fought at the Battle of Eutaw Springs during the American Revolutionary War.[3] He was appointed
lieutenant-colonel of the Third Foot on 7 July 1775 ; colonel in the army on 16 May 1780 ; and promoted major-general
on 28 April 1790. He was granted the colonelcy of the 2nd (The Queen's Royal) Regiment of Foot on 20 November 1793.[4] He served in the Duke of York's army during the Flanders Campaign,[3] commanding the First Brigade of infantry during the retreat to Holland in 1794. He returned home towards the end of the year and ‘fell a sacrifice to an illness contracted in consequence of the fatigues he had undergone’, dying 16 December 1794.[5]