Lemaire will take his final bow on Oct. 1 at the presentation of the Spring-Summer 2015 collection, Hermes said Monday in its announcement.
There was no word about who would replace the designer, whose clothes convey the kind of relaxed, understated luxury befitting the image of the stately Hermes, which got its start in the 19th century as a saddle-maker.
In the statement, Lemaire said he was leaving to tend to his own label.
"My own label is growing in an important way, and now I really want and need to dedicate myself to it fully," the statement quoted the designer as saying.
Lemaire, who joined Hermes in June 2010, called his collaboration with Hermes a "profoundly enriching experience," adding that "I am proud of what we have built together."
Hermes CEO Axel Dumas was more straight-forward in his praise of the partnership.
"Under his (Lemaire's) artistic direction, the metier has renewed its esthetic and produced satisfactory financial results," Dumas said.
Lemaire's appointment at Hermes had raised some eyebrows. The unassuming designer who came from French sportswear label Lacoste was replacing the flamboyant Jean Paul Gaultier — who had toned down his edgy style for the fashionmaker and garnered acclaim.
Sure enough, Lemaire sent out a soft, calm and restful Fall-Winter 2011-12 ready-to-wear collection at his first Hermes show in March 2011. If less spicy than his predecessor, the workmanship was there, and the Hermes-Lemaire team worked for the house, which is still best known for its leather goods.
Hermes' fans will surely wonder what to expect for Lemaire's finale in the fall. A year ago, at his October 2013 show, Lemaire took to the jungle with models in deep greens, blues and nature prints. The clothes, inspired by master painter Henri Rousseau, were classic Lemaire: luxuriant and loose and finely worked.