He was born the son of Captain John Montresor; Henry's brothers were also officers in the Army. From a 2nd Lieutenant in the 23rd Foot in 1780, he progressed to the rank of Lieutenant Colonel of the 18th Foot by 1795. He was then successively promoted Brigadier General (1804), Major General (1810), Lieutenant General (1814) and full General (1837). He saw active service in Corsica 1795 or 1796 commanding the Anglo-Corsican Corps and after the surrender of Calvi was appointed its Commandant. He was in Elba in 1796.