Monfils hit 29 winners and just 10 unforced errors as he clinched the title in his fourth appearance in the final.
"I'm very happy," said Monfils. "I like this tournament so much. I always come back and I finally got it. So I'm just very happy and very proud.
"It's been a while. I was waiting for that moment to get back in shape. In 2016, I was almost on my top and I had a very good year, finishing at number six.
"I couldn't really defend my chances in 2017. I had a long rest and came back strong in 2018, which was a goal. I wouldn't say I was expecting to win the first tournament, but I'm more than happy that I did."