Charles, like his father, made his early career in Brandenburg, attaining the rank of lieutenant-general in 1689. In 1688, he served with his father as a mercenary of the Dutch Republic in the Glorious Revolution which made William III of Orange king of England in 1689. In 1690 he succeeded as Duke when his father was killed at the Battle of the Boyne. From 1691 he served as "General of the troops of his British Majesty in Piedmont", during the Nine Years' War; commanding three regiments of exiled French Huguenots serving in the army of the Duke of Savoy: the regiments of Montauban, Miremont, and Montbrun. These troops were paid by the English government and led by Huguenot officers in English service.
