Known as Fenner, his parents were W. G. Brockway and Frances Elizabeth Abbey.
He attended the School for the Sons of Missionaries, then Blackheath, London (now Eltham College) from 1897 to 1905 where he developed an interest in politics.
Fenner worked as a journalist for a number of publications including the Daily News.
Fenner married Lilla amd they worked together for a number of years.
In 1907 Fenner joined the Independent Labour Party and was later appointed editor of its newspaper the Labour Leader. Fenner was a pacifist and was against British involvement in WWI. He was arrested and jailed for his views against conscription.
After his release from prison Fenner became an active member of the India League, which advocated Indian independence. In 1923 he was made secretary of the Independent Labour Party, becoming chairman a few years later. Fenner also went on to become the first chairperson of War Resisters’ International, from 1926 to 1934. In 1929 Fenner stood for and was elected to Parliament for East Leyton, however he lost his seat in the 1931 election.
Surprisingly for a committed pacifist Fenner did support British participation in the Second World War. He believed fascism could only be dealt with by force: “I could no longer justify pacifism when there was a fascist threat” he later wrote. However he also served as the Chair of the Central Board for Conscientious Objectors throughout the war.
At the end of WWII Fenner returned to Parliament as a Labour MP for Eton and Slough in 1950. There he worked with Tony Benn and joined the left-leaning Tribune Group. Fenner was also a founder member of the Campaign for Nuclear Disarmament.
Fenner accepted a life peerage as The Baron Brockway of Eton and Slough in the Royal County of Berkshire, he took a seat in the House of Lords.