"The sale was signed on Monday evening," the source said, adding that the deal would preserve 1,300 of the 1,500 jobs at the site in Hambach.
Petrochemicals firm Ineos had initially said it planned to build the Grenadier off-roader, its first foray into the automotive industry, in Wales.
But this summer it said it was considering buying Daimler's plant at Hambach instead.
German auto giant Daimler caused surprise when it announced was putting the factory up for sale to try cut costs in the face of losses caused by the Covid-19 pandemic.
It will continue production of an electric-drive Smart and part of a new electric Mercedes SUV at the site until 2024, the source in Hambach said.
The carmaker's departure from Hambach marks the end of an era that began with great fanfare in 1997, when then German chancellor Helmut Kohl and former French president Jacques Chirac inaugurated a plant to produce a mini two-seater city car.
The factory's communications director, Jean-Yves Schmitt, said both Daimler and Ineos would issue statements on the sale later today.
