Stuart was appointed ensign in the 1st Guards in 1794, a lieutenant and captain in 1797. In 1798 he served in Ireland during the Rebellion with the 3rd battalion. In 1799 he accompanied the Battalion in the Anglo-Russian invasion of Holland, and was present in the actions of the 27 August, on 10, 19 September and 2 October. In July 1806 he went to Sicily, and returned in January 1808. In 1807 be attained the rank of Captain and Lieutenant-Colonel. In 1809 he served in the expedition to Walcheren.