[1] He was active in the Independent Labour Party and was a conscientious objector in the First World War, becoming chief lobbyist at Parliament for the No-Conscription Fellowship.

Ammon was Member of Parliament (MP) for Camberwell North 1922–1931 and 1935–1944, unsuccessfully contesting the seat in 1918 and 1931.

He served as Parliamentary Secretary to the Admiralty in 1924 and again in 1929-1931 and was a member of the West African Mission of 1938-1939 and of the Select Committee on National Expenditure, 1939–1944.

He was raised to the peerage as Baron Ammon, of Camberwell in the County of Surrey, in 1944[2] and appointed a Privy Counsellor in 1945.

He was President of the International Arbitration League, vice-president of the Royal National Lifeboat Institution, a governor of the London School of Economics and Dulwich College and chairman of the trustees of Crystal Palace.