During the Napoleonic Wars, Colonel Darling alternated between periods of regimental command and important administrative appointments, leading the 51st Regiment of Foot at the Battle of Corunna and serving as assistant adjutant general during the Walcheren Expedition, before returning to the headquarters at Royal Horse Guards in London, where he served for almost a decade as head of British Army recruiting. In this role, Darling was subsequently promoted to brevet colonel on 25 July 1810, major general on 4 June 1813, and deputy adjutant general in 1814. General Darling was also able to further the careers of his younger brothers Henry and William, and subsequently his nephew Charles; the three brothers all became generals, and Charles also earned a knighthood.