The daughter of commercial traveller Herbert Birkinshaw and Isabella née Garbutt, Mary was born in Bradford.
The family moved when she was four and she was educated at King Edward VI High School for Girls (KEHS) Birmingham, and Bedford College, University of London, graduating with a BA in Philosophy in 1928.
[1] During World War II, Stewart served with the Women's Auxiliary Air Force (WAAF) at locations around the country.
After the war she took an interest in education and psychology and Barbara Wooton encouraged her to become a magistrate in the juvenile courts.
In 1964 she published a short paper titled "Unpaid Public Service" which looked at the role of volunteers on committees.