 In 1922 he joined the Labour Party and was ennobled in 1924 as Baron Arnold, of Hale in the County of Chester, and served as Under-Secretary of State for the Colonies in Ramsay MacDonald's short-lived 1924 Labour Government, and as Paymaster-General from 1929 to 6 March 1931 in Macdonald's second government.In the late 1930s he was a member of the Parliamentary Pacifist Group.He also served as a member of the council of the Anglo-German Fellowship.