Despite his criticism of the Borden government's prosecution of the war as well as its nationalization of Canadian Northern Railway, Carvell broke with Laurier over the issue of conscription opposing Laurier's call for a referendum on the question. Carvell was approached by Borden to cross the floor during the Conscription Crisis and join his government but Carvell initially refused only to change his mind and join the government of Sir Robert Borden on October 17, 1917 as Minister of Public Works in the new Union government. He was re-elected in the 1917 federal election as a Liberal-Unionist MP for Victoria—Carleton by acclamation.