Mary emigrated to Australia with her parents and two brothers at the age of three. She attended a state school in Prospect until she was ten, but not being a good mixer she was transferred to St Cuthbert's Church of England School. From there, she won a scholarship to Walford House school, and this was extended, though during WW II she remembers being threatened with expulsion because of her pacifist views. "An uneasy truce was called". She edited the school magazine in 1941 and in her leaving year won the Tennyson Medal for English.
She enrolled at the University of Adelaide as a cadet at the Barr Smith Library. She won the Tormore House prize for essays and contributed poems and articles to Angry Penguins and Meanjin Papers, and brought out two small volumes of poetry. In 1944 she left Adelaide and lived for a time in Brisbane, where she contributed to Barjai. Always of a deeply religious temperament she underwent what she calls "a sort of psycho-religious re-assessment of my situation". She changed her name officially to Mary Christina St John and from then on all her poems were written under this name.
In 1948 she left Brisbane for Melbourne before leaving Australia for good. She settled in London where she continued her writing and worked as a supply teacher in council schools.
