Playing her first final on the main WTA tour on Sunday, Parks earned a 7-6 (9-7) 7-5 win against last season's WTA Finals champion.
The Atlanta-born world No.79 won two lower-tier WTA 125 titles in December, triumphing in Andorra and the French city of Angers while many players were enjoying an off-season.
Yet this week has been a step up from that level, and 22-year-old Parks capped her run to the final by taking down the top seed and darling of the crowd.
"This title means a lot to me," Parks said. "France has a special part in my heart right now."
A to-and-fro tie-break in the opening set eventually went Parks' way after a stray forehand from Garcia.
A painful fall when running to her right on the baseline meant Parks needed medical attention early in the second set, but she was able to carry on.
Garcia tried to rouse the crowd after clinging to her serve in the eighth game to stay on level terms, and there were unsporting cheers for a double fault from Parks at the start of the ninth.
Yet Parks was not knocked out of her stride, with the player who stood 199th on the rankings this time last year completing the biggest win of her career when Garcia sent down a double fault on match point.
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