Illustration from the 1688 Dutch edition of Description de la Louisiane
Louis Hennepin joined the Franciscans and preached in Halles in Belgium and in Artois. He was then put in charge of a hospital in Maestricht. He was also for a time an army chaplain.
At the request of Louis XIV the Récollets sent four missionaries to New France in May 1675, including Louis Hennepin, accompanied by René Robert Cavelier, Sieur de la Salle. In 1676 Hennepin went to the Indian mission at Fort Frontenac, and from there to the Mohawks.
In 1678, Louis Hennepin was ordered by his provincial superior to accompany La Salle on an expedition to explore the western part of New France. He departed in 1679 with La Salle from Quebec City to construct the 45-ton barque Le Griffon, sail through the Great Lakes, and explore the unknown West.
Louis Hennepin was with La Salle at the construction of Fort Crevecoeur (near present-day Peoria, Illinois) in January 1680. In February, La Salle sent Louis Hennepin and two others as an advance party to search for the Mississippi River. The party followed the Illinois River to its junction with the Mississippi. Shortly thereafter, he was captured by a Sioux war party and carried off for a time into what is now the state of Minnesota.
In September 1680, thanks to Daniel Greysolon, Sieur Du Lhut, Hennepin and the others were given canoes and allowed to leave, eventually returning to Quebec. Louis Hennepin returned to France and was never allowed by his order to return to North America.
Two great waterfalls were brought to the world's attention by Louis Hennepin: Niagara Falls, with the most voluminous flow of any in North America, and the Saint Anthony Falls in what is now Minneapolis, the only natural waterfall on the Mississippi River. In 1683, he published a book about Niagara Falls called A New Discovery. The Regionalist painter Thomas Hart Benton created a mural, "Father Hennepin at Niagara Falls" for the New York Power Authority at Lewiston, New York.