Born in Tavernspite, in Pembrokeshire, Lewis grew up in Rhondda and studied at Treorchy Grammar School.

When he was fourteen, he began working at the local coal mine, joining the South Wales Miners' Federation (SWMF).

In 1921, the SWMF sponsored him to attend the Central Labour College for two years, after which he returned to Rhondda, where he was active in the 1926 UK general strike, although this left him unemployed.

[1] In 1928, Lewis moved to London, to work for the National Council of Labour Colleges as an organiser of tutors.

[1] During World War II, Lewis formed the Ipswich Committee Against Malnutrition, which distributed cheap milk for children and elderly people, a scheme later rolled out nationally.