Top seed Swiatek overcame a second-set crisis and a third-set deficit to beat the unseeded Karolina Muchova 6-2, 5-7, 6-4 and collect her third French Open trophy and fourth Grand Slam title.
A nervous-looking Muchova, competing in her first Grand Slam final, struggled to find her rhythm in the opening set but recovered from a break down in the second to steal five of six games on her way to levelling at one-set all.
An intense deciding set saw the pair trade numerous breaks in an epic finale, with Swiatek using all her experience to find winners when it mattered.
The 22-year-old Pole claimed the last three games of the match which ended in a disappointing double fault from Muchova.
Swiatek dropped her racket, hunched forward and covered her face as she cried.
She becomes the youngest woman with four Grand Slam trophies since Serena Williams was 20 when she got to that number at the 2002 U.S. Open.