William Henry Clinton entered the army in 1784 and served with the Guards in Flanders during the French Revolutionary Wars. He became a lieutenant colonel in 1794 and later an aide to the Duke of York. Staff employment and diplomatic missions accompanied his regimental service: he went to Russia in 1799, became deputy quartermaster general in 1800, and commanded the expedition that occupied Madeira in 1801. He governed the island until its restoration under the Peace of Amiens in 1802.

Clinton subsequently served as military secretary and as quartermaster general in Ireland, and undertook a mission to Sweden in 1807. Promoted major general in 1808, he later commanded troops in the Mediterranean. In eastern Spain he led a division at Castalla in April 1813, where an allied army checked Marshal Suchet. From June 1813 he commanded British forces in that theatre, cooperating with Spanish armies and maintaining pressure around Barcelona as the French withdrew.

He became a lieutenant general in 1814 and received the Order of the Bath in 1815. His career also included parliamentary seats, among them East Retford and Boroughbridge. In December 1826 he took a British force to Portugal during the country's constitutional crisis; the expedition remained until 1828. He reached the rank of general in 1830 and became governor of Chelsea Hospital in 1842. He also held the colonelcy of the 55th Regiment, combining honorary appointments with his long record of command and staff service.