The French winger joined Lens last February after terminating his contract with Mexican side Club America and quickly impressed in the second half of the season.
He registered four goals and three assists in 13 appearances for Les Sang et Or, helping the club lift the Coupe de France, the first major trophy of his career.
Saint-Maximin becomes the second player to leave Lens on a free transfer this summer, following Adrien Thomasson, who has since joined Stade Rennais to remain in Ligue 1.
Further departures are also anticipated, with Malang Sarr’s situation still unresolved despite his contract expiring.
According to L’Equipe, the former Newcastle United winger is now set to join Charlotte FC in MLS, bringing an end to his short but impactful spell in northern France.