The illegitimate son of James, duke of York and Arabella Churchill, sister of John Churchill, later duke of Marlborough, Fitzjames was brought up as a Catholic and became politically significant only for the brief period of his father’s reign. Educated in France from an early age, he had hardly visited England before his arrival in October 1687. It was perhaps a testimony more to the king’s desperate search for willing allies than to the abilities of this virtually unknown and certainly untried teenager that Berwick was almost instantly co-opted to his father’s catholicizing policies. In December 1687, after a dispensation from the penal laws, Berwick replaced Edward Noel, earl of Gainsborough, as lord lieutenant of Hampshire, governor of Portsmouth and the keeper of New Forest for failing to deliver on the three questions.
Despite these failures Berwick remained high in the king’s favour. In July 1688 it was rumoured that he would be given the regiment of the recently deceased James Butler, duke of Ormond. In September several officers refused to co-operate when Berwick tried to incorporate Irish Catholic soldiers into his regiments and had to be court martialled.
Berwick accompanied his father to Ireland where he was involved in actions at Coleraine, Derry, Newry and the Battle of the Boyne. As a result of his activities he was named in the bill introduced into the Commons on 20 June to attaint of high treason certain persons in Ireland, or elsewhere abroad, adhering to the kingdom’s enemies.
After the Treaty of Ryswick, Berwick commanded a regiment in the French service. He continued to assist his father, acting on his behalf in negotiations with Victor Amadeus II, and was present during the exiled king’s last illness. His career was now increasingly centred on military service with France. He served in the French army with distinction after 1702 and became a naturalized Frenchman. His success at the Battle of Almanza earned him a Spanish peerage, the dukedom of Liria and Xerica, and lands to support his new dignity. In November 1707 it was rumoured that Berwick was implicated in a Jacobite plot in Scotland, involving the pretended Prince of Wales and some 30,000 men.
