Frenchman Monfils started quickly to take a comfortable lead but was pegged back by three-time Grand Slam champion Wawrinka, who was appearing in his first final since undergoing ankle surgery in 2017.
But the unseeded world No. 33 was clinical on his serve in the third-set decider as he closed out his eighth ATP career win.
Monfils, who reached the Sofia Open semifinals last week, credited his practice partner Wawrinka for his resurgence, having lost just twice in 11 matches this season.
"You know this win is part of him," said Monfils, who last won an ATP title at the 2018 Qatar Open.
"We've been practising a lot, we've been talking a lot... Sorry I beat you in the final. I hope we can have many more battles."
Monfils established his lead by breaking his opponent early in the opening set. After Wawrinka held his opening service game, Monfils converted his first break point in the third game of the set to edge in front.
He then had two further break-point opportunities in the fifth game before he broke Wawrinka's serve for the second time to seal the set 6-3.
Wawrinka responded well after going behind and raced to a 40-15 lead on Monfils' serve in the opening game of the set. Monfils saved the first two break points and had to save a further two before Wawrinka eventually broke on his fifth break point of the game.
The Swiss then built up a 4-0 lead before he broke Monfils for the third time to win the set 6-1 in just 34 minutes and set up the decider.
Despite winning his opening game to love, Wawrinka was broken by Monfils in the third game of the set before the Frenchman held to lead 3-1.
Monfils served well throughout the third set, hitting 80 percent of his first serves and winning all five of the points on his second serve, and broke Wawrinka for a second time to stretch his lead to 5-2.
Wawrinka showed fight and rallied to set up a break point of his own, but Monfils' serve did not let him down as he won the next three points to clinch the match and seal the title.
Meanwhile, the tournament represents progress for Wawrinka, who was appearing in his first final since he was beaten by Rafael Nadal in the final of the French Open in June 2017.
Information from Reuters contributed to this report