Second-seeded Bartoli overcame the unseeded Li's strong service game to win 77 percent of her second return points and claimed six break points to win in 1 hour, 21 minutes.
Li conceded eight double faults in her first final in 14 months after returning from injury.
Li took a 4-2 lead in the first set and was ahead 30-15 lead in her next service game before she lost consecutive three points in a row - two from double faults - to allow Bartoli to take control and win eight of the next nine games.
Bartoli held serve at 5-3 in the second set, then broke Li at love to complete the victory.
"I feel really good about how I played the whole week,'' Bartoli said. "I had some tough matches, not just today but also in the semifinals. They were both two sets but tough.''
Bartoli, ranked 13th in the world, was playing in her ninth career final.
Since her third and last WTA Tour title at Quebec City in late 2006, Bartoli had lost all four of her finals, including Wimbledon in 2007 and last January in Brisbane, Australia. She followed that with her first quarterfinals at the Australian Open, where she beat then-No. 1 Jelena Jankovic.
Li, ranked 53rd, is a former top-20 player coming back from a right knee injury which kept her out of the Australian Open. She signaled her return to form at Monterrey by beating top-seeded Agnieszka Radwanska of Poland in the first round.
Earlier, Nathalie Dechy of France and Italy's Mara Santangelo won the doubles title with a 6-3, 6-4 victory over Czech pair Iveta Benesova and Barbora Zahlavova Strycova.
