Born in Kilburn, London, Birch became a toolmaker and joined the Amalgamated Engineering Union (AEU).
He became active in the union and also in supporting the Republican government of Spain against the fascist invasion and coup (see Spanish Civil War).
[1] In 1941, Birch worked with Wal Hannington to organise a strike at Swift Scales, an engineering firm in Park Royal.
Journalist Peter Paterson observed: "When I asked him how he could possibly have sided with the 'tankies', so called because of the use of Russian tanks to quell the revolt, he said 'they wanted a trade unionist who could stomach Hungary, and I fitted the bill'.
He met Mao Zedong, Zhou Enlai and Enver Hoxha on visits to China and Albania.