In 1796 Byng became aide-de-camp to General Richard Vyse in the Southern District of Ireland and was wounded during the Irish Rebellion of 1798. He became a major in the 60th Regiment of Foot on 28 December 1799 and a lieutenant-colonel in the 29th Regiment of Foot on 18 March 1800. He transferred to the 3rd Regiment of Foot Guards on 11 August 1804 and took part in the expedition to Hanover in 1805, in the Battle of Copenhagen in August 1807 and, having taken command of the Grenadier Battalion of his Regiment, in the disastrous Walcheren Campaign in Autumn 1809.