Ramsay wasted a three-shot lead before recovering with three straight birdies from the 12th hole at the Golf du Palais Royal to finish with a 10-under 278 total.
Wattel birdied the 17th but settled for par on 18 for a 70.
Six players shared third place at 8 under, including South African George Coetzee, who needed to win to secure a place at the Masters.
“I stood over the putt at the 12th hole and thought, ‘My putter feels great,'” Ramsay said. “I thought, ‘Just go for it, this is your time.'”