His grandfather, Sir Henry Power, was a captain of the Battle-Axe Guards. His father, Captain Lieutenant Bolton Power, served in the 20th Regiment of Foot and fought in all battles of the Seven Years' War, and later in the American Revolutionary War under Guy Carleton and John Burgoyne. Manley Power followed in his forefather's footsteps and was a career soldier, starting as an ensign in his father's old regiment, the 20th Regiment of Foot, on 27 August 1783, when he was either 9 or 10 years old. He served in Halifax, Nova Scotia (1795–1797), Holland (1799), and Minorca (1800). He was part of the force under the command of Sir Ralph Abercromby at the Battle of Alexandria (1801), and later served with the Royal Horse Guards (1803–1805). After rising to Colonel of the 32nd Regiment of Foot,