The Ligue 1 side are set to seal the signing of the Le Havre youngster despite competition from Sunderland, who hoped to add the defender to their rebuilding project
France Under-19 international Mendy made 28 appearances in Ligue 2 last term as Le Havre finished sixth, 10 points off the promotion spots.
Premier League side Sunderland had also come to an agreement over the 19-year-old, but he has seemingly opted to remain on home shores and complete a switch to Stade Velodrome.
"Olympique de Marseille and Le Havre AC have reached an agreement for the transfer of the player Benjamin Mendy," Marseille confirmed on their official website.
Elie Baup's side have already sealed the signature of France international winger Dimitri Payet from Lille in a move worth a reported €10 million.