Will Chamberlain was a journalist on the Daily Citizen, the official newspaper of the Labour Party and Trade Union Congress. In 1914 he joined the newly-formed No-Conscription Fellowship and became its national organising secretary and the first editor of the Fellowship's newspaper, The Tribunal.
Chamberlain recalls fears of the police and threats of conscription which made the NCF organise 'various secret places', for important documents and membership lists to be 'buried in an orchard in Surrey, locked in an unsuspecting city merchant's safe, and at the back of bookshelves in a house of a remote sympathiser.

In May 1916 Chamberlain, with almost the whole national committee, was summoned under the Defence of the Realm Act (DORA) to appear at the London Mansion House for publishing the leaflet 'Repeal the Act' which according to the subpoena contained material prejudicial to the recruitment and discipline of his Majesty's forces. Eight members of the national committee were fined one hundred pounds each. The fines were paid by the Fellowship but most including Chamberlain chose to serve the time in prison. These proceedings showed the government's readiness, partly in response to parliamentary and public pressure to use the provisions of DORA to limit or even eliminate organised agitation against conscription and war.

In October 1916 Chamberlain was called up and refused exemption or to accept Home Office Scheme conditions. In January 1917 he was charged with being absent and handed over to the army; After a spell in Pentonville prison he was sentenced to 2 years hard labour in Wormwood Scrubs and Winchester . He was released from Winchester after the man in the next bed died. He himself was partially, but temporarily, blind. He was released from prison in April 1918 due to ill health.

After the war in in 1921, with Fenner Brockway and others, he was a founder member of the No More War Movement and became its Chairman. The same year while away from home at a meeting he received a telegram to say that his wife had just given birth to a girl, He quickly sent a telegram back: Call her Irene it said, recalls Irene, his daughter, who is a long time PPU member. Irene is a name derived from the Greek for 'peace'.