Born the son of Richard Boyle (born circa 1640) and Elizabeth Boyle (née Ponsonby, daughter of Sir John Ponsonby of Bessborough), Boyle was educated at the University of Oxford. He started his military career as a volunteer in the service of the Duke of Ormonde at the Battle of the Boyne in July 1690 during the Williamite War in Ireland. He also fought, being wounded and becoming a prisoner of war, at the Battle of Landen in July 1693 during the Nine Years' War. He was commissioned as a junior officer in Ormonde's Troop of Horse Guards and cornet in the Army on 16 February 1694 and was promoted to cornet in his regiment and major in the Army in 1697.