Born in the Breton village of Montfort, close to Rennes (France), as an adult Louis identified himself by the place of his Baptism instead of his family name, Grignion. After being educated by the Jesuits and the Sulpicians, he was ordained as a diocesan priest in 1700.
Soon he began preaching parish missions throughout western France. His years of ministering to the poor prompted him to travel and live very simply, sometimes getting him into trouble with Church authorities. In his preaching, which attracted thousands of people back to the faith, Father Louis recommended frequent, even daily, Holy Communion (not the custom then!) and imitation of the Virgin Mary's ongoing acceptance of God's will for her life.
Louis founded the Missionaries of the Company of Mary (for priests and brothers) and the Daughters of Wisdom, who cared especially for the sick. His book, True Devotion to the Blessed Virgin, has become a classic explanation of Marian devotion.
Louis died in Saint-Laurent-sur-Sèvre, where a basilica has been erected in his honor. He was canonized in 1947.