The France international beat Romelu Lukaku, Marcus Rashford and Marouane Fellaini to the gong.
It is the third time Martial has scooped the award following his wins in December 2015 and May 2016.
The striker claimed 41 per cent of the final vote as United fans had their say on their impressive side.
Lukaku came second with 31 per cent, Marouane Fellaini was third with 20 per cent and Marcus Rashford got 8 per cent of the remaining share.
Martial was the standout player in the Carabao Cup against Burton and then the Champions League match at CSKA Moscow.
The 21-year-old scored three goals in September netting in both of the aforementioned games as well as in the 4-0 win over Everton at Old Trafford.
Martial made his 100th appearance for United last weekend against Crystal Palace when he came off the bench.
Paul Pogba claimed the August Player of the Month award.
United return to Premier League action after the international break when they take on Liverpool at Anfield.
The Red Devils are currently second in the table on goal difference with Manchester City in top spot.
