The 33-year-old, who also lifted the trophy in 2010 and 2014, saved all four break points he faced and converted two out of four to secure the win and match compatriot Richard Gasquet‘s haul of three titles.
“I am more than happy to win again in France,” Monfils said. “This is the third time (in Montpellier) and hopefully I can have some more (success).
“It has been a great week. I am very pleased about my performance today. I think I played very solid again and I was very happy with the way I handled the key moments.”
He also improved his head-to-head record against Pospisil to 6-0 en route to the ninth title of his career, although his task became easier after the world No.132 took a tumble and appeared be hampered by a leg injury.
Monfils became the eighth French champion in 10 editions of the ATP 250 event and the world No. 9 will head to Rotterdam to defend his title next week full of confidence.
It was a disappointing day for 29-year-old Pospisil, who was looking to capture a first ATP title in his second final, having returned to form following back surgery in January 2019.
“It was an incredible week,” he said. “I had great wins and I feel like I am definitely improving week-by-week. I will try to rest now, take a couple of days easy and get ready for the next event.”