The Frenchman, who was nominated for the prize along with teammates Kieran Trippier and Fabian Schär, was shortlisted for his stunning volley against Wolves which rescued a point for the Magpies at Molineux.
Saint-Maximin's first-time effort after a clearance dropped fortuitously into his path saw him pick up the first award of the new season, beating off competition from Trippier - for his free kick against Manchester City - and Schär, whose thumping strike in the opening-day win over Nottingham Forest earned him a nomination.
United's number ten also pipped Brentford's Bryan Mbeumo, Arsenal's Gabriel Jesus, Chelsea's Kalidou Koulibaly, Luis Diaz of Liverpool and William Saliba of Arsenal to the award and became the second Newcastle player to win it in 2022, after Miguel Almirón collected the gong in May for his finish against Crystal Palace.
"It's a tough trophy to win so I'm very proud," said Saint-Maximin. "It was a nice goal, but it's always very difficult to win this trophy. You can see many players scored a goal goal, even at Newcastle with Faby and Tripps, so that's why I'm very proud to win that trophy and get a point for my team."