Médard Chouart was born in Charly-sur-Marne, Champagne province, France, to Médard Chouart, his father and Marie Poirier. He also had a cousin named Médard Chouart. He later called himself Sieur des Groseilliers after a farm his parents managed in Bassevelle. He was reported to have immigrated to New France in 1641 at age 23, but according to Historian Grace Lee Nute, this has never been proven. He became a "donné" or lay helper at the Jesuit missions in the Huron region near present-day Simcoe County, Ontario. Here he learned the skills of a coureur des bois. In 1646, Groseilliers fought with the Huron against the Iroquois.