Len Fox grew up in Melbourne's east, and attended the University of Melbourne. He graduated with a science major and a Diploma of Education, and subsequently taught at Scotch College, Melbourne, from 1928-1932. His interest in progressive educational policies led him to England in 1933.
Fox returned to Melbourne in 1934, where he joined the Communist Party, and became State secretary in Victoria of the Movement against War and Fascism the following year. In 1939, Fox relocated to Sydney, where he worked on two political newspapers between 1940 and 1955: the Labor Party's Progress and the communist Tribune.
Fox and his wife, the playwright Mona Brand (q.v.), lived in Hanoi during 1956 and 1957. On their return to Sydney in 1958, Fox worked as a journalist for Common Cause, the Miners' Federation newspaper, holding the position of editor from 1965-1970, before retiring from journalism.
Fox wrote poetry, short stories, children's literature and drama. Much of his work explores his interest in social issues, Aboriginal people and Vietnam. He is the author of numerous widely-read pamphlets about politics, economics and history, and was an early proponent of creating a distinctive Australian cultural identity. He edited a history of the Fellowship of Australian Writers, Dream at a Graveside (1988) and also wrote a biography of his uncle, the artist E. Phillips Fox.