Christophe Galtier's Lille sits second in the top flight on 69 points with three games remaining but, thanks to Montpellier's 1-0 win at Stade Geoffroy-Guichard, its place in the top three is now secured.
With only Lyon capable of catching up, Lille — Ligue 1 champion in 2010/2011 — is guaranteed a spot at least in the UEFA Champions League qualifiers, a remarkable turnaround in fortunes after its 17th-place finish in Ligue 1 last term.
Key to Lille's successful season has been the form of Nicolas Pepe, who has scored 20 goals in 35 Ligue 1 appearances.
Heading into Ligue 1 for next season is Brest, which beat Niort 3-0 to move four points clear of third-place Troyes in Ligue 2 with just one game left. It joins Ligue 2 champion Metz in securing promotion.
It is not yet decided which two teams will be automatically relegated from Ligue 1, with Guingamp and Dijon occupying the drop zone, although both remain in with a chance of survival.