FitzRoy was granted brevet rank as colonel on 26 January 1797, and in 1799 commanded the grenadier company of the 1st Foot Guards during the expedition to Holland. On 5 January 1801 he was made an extra equerry to the King. He was later appointed aide-de-camp to the King, and major-general on 25 September 1803. He served on the staff of the Eastern District, and from 1804 of the Western District. On 25 March 1805 he was made colonel of the 25th Regiment of Foot, on 27 August 1809 appointed regular equerry to the King, and on 25 July 1810 he was promoted lieutenant-general. He had resigned his post as an equerry by 11 October 1811, when he was replaced by Brent Spencer. On 21 September 1816 he married Eliza (née Barlow), widow of Clavering Savage; they had no children. He was promoted to general on 19 July 1821.