Born in Bethnal Green, Newens was educated at Buckhurst Hill County High School.
At UCL, he met Anil Moonesinghe, a Sri Lankan Trotskyist, who was later to become a Cabinet Minister in Sri Lanka, and joined the Socialist Review Group led by Tony Cliff, a former member of the Revolutionary Communist Party (RCP), which later became the Socialist Workers Party (SWP); he left this group in 1959.
He held several posts in the National Union of Teachers and was chairman of the Movement for Colonial Freedom and president of the London Co-operative Society.
Newens was an active trade unionist, and wrote numerous pamphlets and books, including The Case Against Nato (1972), Third World: Change or Chaos (1977), A History of Struggle: 50th Anniversary of Liberation, formerly the Movement for Colonial Freedom (2004) and Nicolae Ceausescu: The Man, His Ideas and His Socialist Achievements (1972).
His autobiography, In Quest of a Fairer Society: My Life and Politics, was published in November 2013 by The Memoir Club.