The 31-year-old Mahut topped his Swiss opponent 6-3, 6-4 for his first career ATP title.
Mahut, playing in the third title match of his career and first since 2007, heads into Wimbledon with some momentum.
Wawrinka was seeking his first ATP title as well. He was runner-up at the Madrid Masters this year.
2014: The Year in Fashion [PHOTOS]
UPI Sports Results for September 19, 2014