Transferred to the 35th Regiment of Foot in 1758, Morris served in Fort Frederick in Nova Scotia; he led the Cape Sable Campaign against the Acadians. Morris joined the Louisbourg Grenadiers, a special corps made up of the Grenadiers of the 22nd, 40th and 45th Regiments, during General James Wolfe's invasion of French Quebec where he participated in the Battle of the Plains of Abraham on 13 September 1759. During the siege of Louisbourg, Grenadiers suffered a loss of fifty-five killed and wounded. In May 1760, Morris was promoted to lieutenant-colonel of the 47th Regiment of Foot shortly after the Battle of Sainte-Foy, and participated in General Jeffery Amherst's assault and capture of Montreal on 8 September 1760 ending French rule in North America.