Born in Cornwall, Williams migrated to South Africa in 1929. He taught English literature at prestigious schools in Johannesburg, and volunteered to fight in WWII. During and after the war Williams was a leading activist in the anti-fascist Springbok League, in the South African Communist Party, and in the 1950s in the African Nationa Congress-aligned Congress of Democrats.

Williams was a prominent theatre director, his productions including the anti-apartheid Kimberly Train in 1959. Driven "underground" with Nelson Mandela when the latter re-entered the country illegally from Botswana as head of the ANC's armed wing, Williams was arrested near Pietermaritzburg in 1962.

He fled with his Scottish boyfriend into exile in the UK and died there.He has been credited by ANC leaders with having had a profound impact on their understanding of homosexuality, laying the groundwork for the ANC's adoption of gay rights policies in the late 1980s.