Pierre-Gabriel Marest (sometimes Maret, Marais; October 14, 1662 – September 15, 1714, in Kaskaskia (Randolph County, Illinois)) was a French Jesuit missionary in Canada.
In 1694 Marest was sent to Canada and chosen chaplain of an expedition under Pierre Le Moyne d'Iberville that was being outfitted to try to take the Hudson Bay region from the English.
Marest busied himself learning the native language, apparently from word lists supplied him before his arrival.
In September 1696 Hudson's Bay Company ships retook the fort, and Marest was himself taken prisoner.
In 1698 he was assigned to the mission of the Immaculate Conception in the Illinois country (then under French control as part of Louisiana).
The mission had been founded by Father Jacques Gravier and served a confederacy of tribes, among them the Kaskaskias, Cahokias, Peorias, Tamaroas and Michigameas.
After four days journey they stopped at the Cahokia (or Tamaroa) mission at the mouth of the Des Pères River.
The new community faced problems from Canadian traders, who supplied spirits and seduced the women.
Marest asked for help from Jean-Baptiste Le Moyne de Bienville, governor of Louisiana, who sent a sergeant and 12 men.
As the result of infection from an arrow wound inflicted by the Peorias, Gravier left the Illinois country in 1705 to return to France.
He spent a fortnight in the Peoria village, and then continued on to the mission to the Potawatomis on the St. Joseph River, where his brother met him.
He reported also on the life of the missionaries: "our life is passed in threading dense forests, in climbing mountains, in crossing lakes and rivers in canoes...." Marest died at Kaskaskia in September 1714 during an epidemic, after an illness of only eight days.