Louise de Marillac, also called Louise Le Gras, (August 12, 1591 - March 15, 1660) was the co-founder, with Saint Vincent de Paul, of the Daughters of Charity. As the first leader of the Daughters, she was devoted to serving Jesus Christ through work with the poor and corporal and spiritual works of mercy. By the time she died in 1660, there were more than forty houses of the Daughters of Charity in France, and the sick poor were cared for in their own dwellings in twenty-six parishes in Paris.

Louise was born out of wedlock, and never knew her mother. her father, Louis de Marillac, was Lord of Ferrires, and claimed her as his daughter though not his heir. She later married Antoine Le Gras, secretary to Queen Marie, though he died died twelve years after marriage. Louise met Vincent de Paul shortly after Antoine's death, began her work with Vincent's Confraternities of Charity in 1629, and co-founded the Daughters of Charity in 1633.

Louise de Marillac was canonized by Pope Pius XI on March 11, 1934. Her feast day is March 15.