French-Canadian explorer and cartographer who, with Father Jacques Marquette (Marquette, Jacques), was the first white man to traverse the Mississippi River from its confluence with the Wisconsin to the mouth of the Arkansas River in Arkansas.

Jolliet received a Jesuit education in New France (now in Canada) but left his seminary in 1667 and went to France. The following year he returned to New France to work in the fur trade. In 1672 he was commissioned by the governor of New France to explore the Mississippi, and he was joined by Marquette. On May 17, 1673, the party set out in two birchbark canoes from Michilimackinac (St. Ignace, Mich.) for Green Bay, on Lake Michigan. Continuing up the Fox River in central Wisconsin and down the Wisconsin, they entered the Mississippi about a month later. Pausing along the way to make notes, to hunt, and to glean scraps of information from Indians, they arrived in July at the Quapaw Indian village (40 miles north of present Arkansas City, Ark.) at the mouth of the Arkansas River. From personal observations and from the friendly Quapaw Indians, they concluded that the Mississippi flowed south into the Gulf of Mexico—not, as they had hoped, into the Pacific Ocean.

In July the party returned homeward via the Illinois River and Green Bay. Their journey is described in Marquette's journal, which has survived.

Jolliet later travelled to Hudson Bay, the Labrador coast, and a number of Canadian rivers. In 1697 he was made royal hydrographer of New France.