The rural parish of Saint-Paul-l'Ermite was established in 1856. The municipality of the same name was created in 1973 over part of the original territory. It changed its name to Le Gardeur five years later. (Pierre Le Gardeur, Sieur de Repentigny, was the region's first feudal lord, under letters-patent granted in 1647 to the Compagnie des cent associés.) The parish and its church are still active.
Le Gardeur's main population is concentrated near the L'Assomption River in the southernmost part of the city, bordering the rest of Repentigny, and the Saint Lawrence River. The northern part is mostly farmland, and is being developed as a suburban area. This is where the March 2006 announced AMTRepentigny-Mascouche Linecommuter train service that is scheduled to begin service in 2010 will turn off the existing Canadian National line onto its own right of way heading towards Terrebonne.