Swiatek, 19, won the 84-minute match 6-4, 6-1 for her country's first major tennis title. She had three aces, 25 winners and 17 unforced errors in the victory. Kenin, 21, had three aces, 10 winners and 23 errors.
"I'm so happy that my family was here, finally. It's crazy. I'm just overwhelmed," Swiatek said after her win.
Swiatek sprinted out to a 3-0 lead in the first set before Kenin won the fourth game of the match. Kenin went on to tie the set at 3-3 before Swiatek won the seventh and eighth games. Kenin broke Swiatek to win the ninth game. Swiatek broke Kenin for the final point of the first set.
Kenin broke Swiatek to win the first game of the second set. Swiatek responded by winning the next six games to win the match. She won three break points down the stretch.
Swiatek -- ranked No. 54 -- is the lowest-ranked women's player to win the French Open since rankings began in 1975. She claimed a $1.9 million prize for her victory.
She lost just 28 games in seven matches and never lost a set during her run at Roland Garros.
Swiatek beat Marketa Vondrousova on Sep. 28 in the first round of the Grand Slam. She then beat Hsieh Su-wei and Eugenie Bouchard before she knocked off No. 1 seed Simona Halep in the fourth round. Swiatek beat Martina Trevisan in the quarterfinals and defeated Nadia Podoroska in the semifinals.
Kenin -- the No. 4 seed -- began the tournament with a win over Ludmilla Samsonova. She then beat Ana Bogdan and Irina Bara before her win over France's Fiona Ferro in the fourth round.
Kenin beat fellow American Danielle Collins in the quarterfinals before she beat No. 7 Petra Kvitova in the semifinals to advance to the final match with her unranked foe.
Nadal, 34, will attempt to win a record-extending 13th title on the clay courts. Djokovic, 33, will attempt to win his second French Open crown.
"It's crazy for me because I was watching every year how Rafa lifts the trophy," Swiatek said. "It's crazy that I'm in the same place, but I want to thank all the fans and the people who are watching in Poland. I know it's pretty crazy back home."