Ruth Frow, née Engel, was born in the north London suburb of Mill Hill to a mixed Anglo-Jewish and Irish family. She was educated at Downhurst, a private high school in Hendon. At the outbreak of World War II, when she was 17, she left school and enlisted in the Women's Auxiliary Air Force (WAAFs). She spent the war in Fighter Command on the Kentish coast, where she was introduced to left-wing political views. In the 1945 general election, she and her first husband campaigned for the Labour Party, and then joined the Communist Party. Her interest in social reform led her to become a teacher. Throughout the 1950s, she was active in peace campaigns and in labor unions. In 1961, she married Edmund Frow, a toolmaker and shop steward whom she had met at a Communist Party school in Sussex nearly 10 years earlier. Both loved books and they compiled an extensive library in their home in Salford, Manchester with particular focus on labor history that became known as the Working Class Movement Library. It became a major resource for historians and academics, who were welcome to visit. She wrote several books of her own on labor history, including Political Women: 1800-1950 (1989). During bitter factional rivalries of the 1980s, Ruth was expelled from the Communist Party, but she continued to manage the library after Edmund Frow's death.