McDowell took his fifth European Tour title after finishing the event at 15-under 269, three strokes better than Rhys Davies, who closed with a 9-under 62 -- a course record -- to claim sole possession of second place at minus-12.
The Northern Irishman began the back nine with a pair of birdies, and when Davies committed a rare stumble with a bogey on the tough 16th, McDowell seized the opportunity.
McDowell's 63 gained him his first victory since the 2008 Scottish Open and the $420,000 first prize, while Davies was a European Tour runner-up for the second week running.
Luke Donald had another good day, registering a 6-under 65 to stake out third place at 10-under 274.
Robert Rock (66), Edoardo Molinari (67) and Stephen Gallacher (69) finished in a three-way for fourth at minus-9.
Meanwhile, third-round leader Marcel Siem ran into trouble Sunday, falling to a 3-over 74, leaving him alone in seventh place at minus-eight.