By the end of the war he had risen to colonel and king's aide-de-camp, and he then moved to command the forces in Nova Scotia (1783–89), where he was influential in the creation of the new colony of New Brunswick, and then the Chatham Barracks (1789–93).

Next he was quartermaster-general on the duke of York's staff in Flanders to replace the recently killed James Moncrief (1793–95) and fought in the Netherlands theatre of the French Revolutionary Wars.

He then served as Inspector-General of the recruiting service (1795–99), Colonel of the 10th (North Lincolnshire) Regiment (1795–1811), Lieutenant-governor of Minorca (1799–1801) following its capture from the French, commander in chief of all British Mediterranean forces outside Gibraltar (1801–03, replacing General Sir Ralph Abercromby fatally wounded at the battle of Alexandria) and finally Commander-in-Chief, Ireland (1803).

In Ireland he was caught off-guard by Robert Emmet's Dublin uprising (23 July 1803) and was quickly replaced by Lieutenant-General Cathcart, whose appointment was gazetted on 20 October.

With his health weakening, Fox passed active command of the force to his deputy, Lieutenant-General Sir John Moore.