Howard was gazetted to an ensigncy in the Coldstream Guards, 21 April 1786, and served with his regiment in Flanders from February 1793 to May 1795, being wounded at St. Amand 8 May 1793. He was promoted lieutenant and captain 25 April 1793 (acting as adjutant of his regiment from December 1793 to December 1797), captain-lieutenant and lieutenant-colonel 30 December 1797, and brigade-major to the foot-guards 17 April 1798, in which capacity he served throughout the Irish rebellion of that year and the Duke of York's expedition to Holland in 1799. He was present in every action of the last-named campaign. He was gazetted captain and lieutenant-colonel 25 July 1799, and was connected with the foreign troops in the English service as deputy inspector-general, inspector-general, and commandant of the foreign depôt. This latter office he resigned on being appointed colonel and aide-de-camp to the king, 1 January 1805. He became second major of his regiment 4 August 1808, and major-general 25 July 1810.