Gwen Nash was born in Cairo, Egypt, in 1904, of missionary parents. After World War I the family migrated to Sydney and Gwen studied medicine at Sydney University, where she was one of only seven women in a class of 56. After graduation, she worked at Prince Alfred Hospital, Crown Street Women's Hospital and the Children's Hospital. In 1932 she enrolled at the Melbourne Bible Institute, where she met her husband, Laurence Nash. When they were married in 1933 she followed him to Hong Kong, where she became Director of Women's Medical Services.
Gwen returned to Australia at the outbreak of World War II when her husband joined the Royal Australian Navy. During the war Gwen raised three children and continued working in general practice in East Melbourne and at the Freemasons and Queen Victoria hospitals.