At the age of fourteen, she joined the Marianites of Saint-Laurent, Montreal, a feminine branch of the Holy Cross Congregation. In spite of poor health, she was admitted to pronounce her vows by the founder, Father Basile Moreau. She received the name of Sister Marie de Sainte-Léonie and taught for several years.

She was attracted to give her support to the ministry of priests, but obedience had another line of work drawn out for her. She taught in the Montreal area until 1862, after which she was sent at the Saint Vincent-de-Paul orphanage in New York.

In 1870, believing that her dream would be fulfilled, she chose to transfer to the American community of the Holy Cross Sisters in Indiana.

Once in Indiana, Sister Marie de Sainte-Léonie taught needlework and French at St. Mary’s Academy. Her wish to dedicate herself to the clergy is put on hold, but her twelve year stay in the United States permitted her to command the English language.

In the fall of 1874, she was sent from Indiana to Memramcook, New Brunswick, to supervise the religious staff and also the young Acadians who did the housework at St. Joseph’s College, then directed by Father Camille Lefebvre, C.S.C. Very quickly, this place became a bustling vocation site as many generous young women gathered around Sister Léonie.

In 1880, the Institute of the Little Sisters of the Holy Family was officially founded by Sister Léonie to support and to collaborate with the Holy Cross Religious in the field of education.

In 1895, the death of Father Lefebvre, who assisted the community, left this work full of promise without canonical approval.

Physically, Mother Marie-Leonie was short of stature, and her dignified appearance was remarkable. Her clear complexion, her profound eyes, her radiant and smiling face attracted everyone. Morally, she was a woman with a big heart, warm cordiality and compassion towards each human misery. All sorrow was hers; she tried hard to relieve and to console everyone. Bishop Paul LaRocque said that she spent her life giving of herself: “She always had her arms open, her heart in hand and a smile on her lips, welcoming everyone as though they were God himself. She was all heart.”

Her heart and bones are preciously preserved in an Oratory opened in 1985, next to the chapel of the General House at Sherbrooke, Quebec.