Joan Allen grew up on a farm in Kendenup, Western Australia. She trained as a journalist and worked on the West Australian and the Daily News. She was politically active from the 1920s and a prominent member of the Western Australian branch of the Communist Party of Australia from 1939. Her immediate circle of friends included other journalists, artists and writers often active in leftwing politics. She was strongly influenced by Mary Durack, Bill Irwin, Ray Oldham and Katharine Susannah Prichard (qq.v.). Allen saw Marxism as the only response possible to issues surrounding the Spanish Civil War. In 1938, she and her first husband, Peter Thomas, also a journalist, went to England and Germany where they saw the appeasement of Chamberlain and the militarisation of Germany at close hand. She was an active participant in demonstrations against Australian politician Robert Menzies's support for appeasement.
After the war, Allen divorced and remarried, this time to Victor Williams (q.v.) She was a member of the Modern Women's Club, the Western Australian Council for Equal Pay and Opportunity, the Union of Australian Women, the Ban the Bomb Movement and the International Women's Day Committee. In the 1950s Williams campaigned for nuclear disarmament and established a locally based Waterside Workers Federation Women's Committee to support strike action. In the early 1970s she participated in the Women's Liberation Movement and the Women's Electoral Lobby and from 1980 was the Secretary of the Australian Peace Committee. She lived in Melbourne, Moscow, London and Albany, Western Australia.
Williams, who wrote and published as 'Justina Williams', was a member of the Fellowship of Australian Writers. She also wrote The First Furrow (1976), a history of the West Australian branch of the Communist Party of Australia to 1942 and Trade Unionism (1978), part of the Australian Life series for school children.