She was born Marie-Marguerite Dufrost de Lajemmerais in 1701 at Varennes, Quebec, oldest daughter of Christophe du Frost, Sieur de la Gesmerays (1661–1708) and Marie-Renée Gaultier de Varennes. (Pursuant to Quebec naming conventions, she would have always been known as Marguerite, not Marie.) Her father died when she was a young girl. Despite her family's poverty, at age 11 she was able to attend the Ursuline convent in Quebec City for two years before returning home to teach her younger brothers and sisters. Marguerite's impending marriage to a scion of Varennes society was foiled by her mother's marriage below her class to Timothy Sullivan, an Irish doctor who was seen by the townspeople as a disreputable foreigner. On August 12, 1722, at Notre-Dame Basilica in Montreal, she married François d'Youville, a bootlegger who sold liquor illegally to Indians in exchange for furs and who frequently left home for long periods for parts unknown. Despite this, the couple eventually had six children before François died in 1730. By age 30 she had suffered the loss of her father, husband and four of her six children, who died in infancy. Marguerite experienced a religious renewal during her marriage. "In all these sufferings Marguerite grew in her belief of God's presence in her life and His tender love for every human person. She, in turn, wanted to make known His compassionate love to all. She undertook many charitable works with complete trust in God, whom she loved as a Father."
Marguerite and three other women founded in 1737 a religious association to provide a home for the poor in Montreal. At first the home only housed four or five members, but it grew as the women raised funds. As their actions went against the social conventions of the day, d'Youville and her colleagues were mocked by their friends and relatives and even by the poor they helped. Some called them "les grises", which can mean "the grey women" but which also means "the drunken women", in reference to d'Youville's late husband. By 1744 the association had become a religious order with a rule and a formal community. In 1747 they were granted a charter to operate the General Hospital of Montreal, which by that time was in ruins and heavily in debt. d'Youville and her fellow workers brought the hospital back into financial security, but the hospital was destroyed by fire in 1765. The order rebuilt the hospital soon after. By this time, the order was commonly known as the "Grey Nuns of Montreal" after the nickname given to the nuns in ridicule years earlier. Years later, as the order expanded to other cities, the order became known simply as the "Grey Nuns".
Marguerite d'Youville died in 1771 at the General Hospital. In 1959, she was beatified by Pope John XXIII, who called her "Mother of Universal Charity", and was canonized in 1990 by Pope John Paul II. She is the first native-born Canadian to be elevated to sainthood by the Roman Catholic Church. Her feast day is October 16. In 1961, a shrine was built in her birthplace of Varennes. Today, it is the site of a permanent exhibit about the life and works of Marguerite. The review process included a medically inexplicable cure of acute myeloid leukemia after relapse. The woman is the only known long-term survivor in the world, having lived more than 40 years from a condition that typically kills people in 18 months.
A large number of Roman Catholic churches, schools, women's shelters, charity shops, and other institutions in Canada and worldwide are named after St. Marguerite d'Youville. Most notably, the renowned academic institution of higher learning, D'Youville College in Buffalo, NY, is named after her. The D'Youville Academy at Plattsburgh, New York was founded in 1860.
Sir Louis-Amable Jetté’s wife, Lady Jetté, wrote a biography of Saint Marie-Marguerite d'Youville.