The 21-year-old ninth seed recovered from dropping the opening game to the top seed and Olympic champion to complete an incredible 17-21, 21-17, 21-18 victory and earn her country its first ever major title in the sport.
Li had rarely looked in trouble during her run to the final and she again looked at ease with her terrific stroke play proving too much for the tenacious Marin in the opening game.
This time though Marin responded by taking the attack to her opponent for whom the nerves perhaps began to take hold as Li began to misfire more regularly with Marin levelling the contest on the first of three set points.
The Chinese regrouped in the third game and inched 14-11 ahead but once more Marin came roaring back and moved to within a point of an improbable victory as Li fired long.