The Cape Verde international began his career at Batuque before moving to Le Havre in 2008, and went on to make 97 appearances for the Ligue 2 side, scoring 19 goals during his four-year stint.
Speaking on RMC about his future, Mendes explained: "I spent many happy years at Le Havre, but today I want something else.
"I talked to my president and I told him I want to go to Lille. Lille is my priority."
Les Dogues have looked to reinforce their strikeforce following Eden Hazard's €41 million move to Chelsea, and Mendes looks set to be their third attacking signing of the transfer window after Marvin Martin and Salomon Kalou were also snapped up.