The Super Eagles striker claimed 45% of total votes to emerge tops ahead of Monaco’s Islam Slimani (37%) second and Nantes’ Nicolas Pallois (18%) on third spot.
The former Golden Eaglets ace will now takes over from Rennes midfielder Eduardo Camavinga who claimed the award in August.
The 20-year-old scored two goals in four league appearances for Lille in September.
He was on target in Lille’s 2-1 win against Angers SCO and the 2-0 victory at home to Strasbourg.
Osimhen took to twitter to express his gratitude after the big announcement, he said: “Player of the month of September. Major thanks to those who voted for me, I appreciate each and every one you, special gratitude go to my family, teammates and my loved ones. GOD is the greatest. We move.”
Osimhen joined Lille this summer from Belgian Sporting Charleroi and has scored seven goals in nine appearances in the Ligue 1.