McDowell began the final round with a one-shot lead and a closing level-par 70 in tough scoring conditions at Royal Greens Golf and Country Club was enough to seal a first European Tour title since 2014.
The win is set to lift McDowell from 104th in the world rankings to back inside the top 50, less than a year after the 2010 US Open champion found himself a lowly 257th.
Defending champion Dustin Johnson made his second eagle of the day on the 18th to finish two shots behind McDowell on 10 under for the tournament, with Phil Mickelson, Thomas Pieters and Gavin Green a stroke further back.
An emotional McDowell fought back tears as he told Sky Sports: "It's tough to win on a course that doesn't fit your eye but this is a sweet one.
"If my kids are watching at home I love you guys, and my wife obviously. I can't wait to get home and see them."
The 40-year-old Northern Irishman added: "A big goal this year was to be back in the top 50, it's come a little faster than I expected. I've been working hard the last year and a half to try and get myself back up there one more time just to be out there playing against these guys.
"The game of golf is in such great shape, so many great players, it's so exciting to be a top player in the world and I want to be back up there again.
"I've got young kids at home and I want to show them that dad's tough and dad can do it. I don't want to have to pull up the YouTube videos."