Howard joined the Army as an ensign on 4 February 1703. During the War of the Spanish Succession he served in the Netherlands and Germany under the Duke of Marlborough, and in 1707 was present as a captain in Wade's Regiment of Foot at the Battle of Almanza, where he was taken prisoner. He was a prisoner of war in France for two years, but was promoted lieutenant-colonel of the 24th Regiment of Foot in 1708 and served at the Battle of Brihuega in 1710, where he was again captured. On 15 November 1711 he was granted brevet rank as a colonel of Foot. Howard was dismissed for his political opinions, but was reinstated by King George I, and in 1717 he purchased the colonelcy of the 24th Regiment of Foot, succeeding General Primrose.