Seymour became commanding officer of the fifth-rate HMS "Fortunée" in June 1812 and of the fifth-rate HMS "Leonidas" in January 1813 during the War of 1812. In HMS "Leonidas" he captured the privateer USS "Paul Jones" in May 1813. He was appointed a Companion of the Order of the Bath on 4 June 1815. He became Serjeant-at-Arms to the House of Lords in 1818 and was given a short leave of absence to undertake a tour as commanding officer of the fifth-rate HMS "Briton" on "particular service" in 1827. He was appointed a Knight Commander of the Royal Guelphic Order in 1831, awarded a British knighthood on 23 March 1831 and advanced to Knight Grand Cross of the Royal Guelphic Order on 9 December 1834. In June 1837 he attended the funeral of King William IV, Seymour's last act as Master of the Robes to the King.