Sister Mary Leo’s Auckland childhood was in a family which had played an active part in the city’s cultural and commercial development since its establishment. She was educated by the Sisters of Mercy, and early in her life showed exceptional musical talent. Her decision to train as a teacher seemed natural, and she taught at Onerahi and Hawkes Bay, communicating love of music to her pupils and teaching private classes in dancing, elocution, and singing. She realised her vocation in her teenage years, but entered the Order of the Sisters of Mercy at twenty-eight. While occupied in the regular work of her order in tending to the sick and needy, her outstanding skills as a music teacher became evident and she was encouraged to develop these talents to the glory of God. She developed the already strong musical tradition of St Mary’s College, Auckland, with its orchestra, choirs, and individual tuition, and also conducted the Sisters’ Choir. From 1934 the college offered private tuition and her reputation as a vocal coach was given room to flourish.

Sister Mary Leo was a perfectionist with great vitality, who demanded the best from her students but required the same dedication from herself. From 1950 on honours and plaudits followed the remarkable success of many of her students - Elisabeth Hellawell, Kiri Te Kanawa, Heather Begg, Malvina Major and Patricia Price, to name only a few. Yet she remained modest and devoted to her life as a nun, giving of her talents to others.