Called "tipsy women" because of the d'Youvilles' alleged profits from brandy trafficking, in 1747 they were put in charge of the bankrupt Hôpital Général of Montréal, founded in 1692 by François Charon de La Barre. They reorganized it into a hospice for aged men and women, foundlings, orphans and "fallen women." In 1750 civil and ecclesiastical authorities decided to unite it with the Hôpital Général of Québec, but the Sulpicians interceded in Paris, and on 3 June 1753 Louis XV gave the community legal status and title to the hospital.
In 1755 the women finally began their life as the Sisters of Charity of the Hôpital Général, or the GREY NUNS (Soeurs grises). They developed various enterprises including farms, an orchard, a mill and a bakery to finance their work. During the smallpox epidemic of 1755 and the Seven Years' War, their institution truly became a hospital. Mère d'Youville faced disappointments, however; her family returned to France at the Conquest, and her hospital burned in 1765. After years of failing health she died in 1771.
Many Montréalers attested to her prophetic gifts and miraculous healing powers. Her spirituality and sacrificial life were officially recognized by Rome. She was the first Canadian-born person to be beatified and was canonized in 1990.