D'Oyly was lightly wounded at the Battle of Lincelles, and served with the 1st Regiment of Foot Guards in Flanders from 1794 to 1795. He was promoted to major general on 3 October 1794. Promoted from second to first major of the regiment on 3 October 1797, he was then appointed the regimental lieutenant colonel on 11 October. He served as a brigade commander in the 1799 Anglo-Russian expedition to the Netherlands. He became colonel commandant of the 2nd Battalion, 15th Regiment of Foot on 18 November 1799. D'Oyly was promoted to lieutenant general on 1 January 1801. He went on half-pay in 1802, when the 2nd Battalion was disbanded, and was appointed colonel of the 67th (South Hampshire) Regiment of Foot on 25 February 1803.