After a topsy-turvy opening set that Belarusian Sabalenka edged after a tiebreak, second seed Gauff responded with an immediate break and won the second set 6-2.
And the 21-year-old American, who lost the 2022 French Open final as an 18-year-old, maintained her momentum to serve out for victory in the deciding set 6-7 (7-5), 6-2, 6-4 for her second Grand Slam title and her first on clay.
Gauff became the first American woman to capture the singles title in Paris since Serena Williams in 2015 and the youngest from the United States to achieve the feat since her decorated compatriot in 2002.
It was the first world No.1 vs. No. 2 final at Roland Garros since 2013, when Serena defeated Maria Sharapova, and just the second in the last 30 years.
Paris was guaranteed a new champion but the first clash between the top two women in the world rankings in a major final since the 2018 Australian Open initially failed to live up to its billing on a blustery Court Philippe Chatrier.
After Sabalenka sent a backhand wide on Gauff's second match point, the young USA star fell onto her back, covering her face with both hands before resting her forehand on the clay.
After greeting Sabalenka at the net, she then hugged film director Spike Lee and celebrated with her entourage, three years after she lost in her first final at Roland-Garros.
Sabalenka started the deciding set strongly, sticking to her high-risk approach to hold her first service game.
Gauff responded by raising her level, winning a superb rally in the third game that drew loud cheers and applause from the crowd.
In her on-court speech, she admitted that defeat in 2022 had put her in a "dark place" and then thanked the fans on Court-Philippe Chatrier, who were rooting mostly for her.
After collecting the Suzanne Lenglen Cup, she admitted: "I didn't think honestly that I could do it.
"I was going through a lot of things when I lost this final three years ago. I'm just happy to be here.
"I'd like to congratulate Aryna. You're a fighter. You're the number one player in the world. Today was a tough match, but you deserve all the results you've been having. Every time we play, it's such a tough match.
"The crowd helped me today. You guys were cheering for me so hard and I don't know what I do to deserve such support from the French crowd. I didn't think I could do it."
After an intense exchange of drop shots, Gauff hit a lob that Sabalenka chased down before attempting a shot between her legs — only for Gauff to intercept it at the net and finish with a winner.
Gauff was consistent from the baseline and earned a break point which she converted when Sabalenka double-faulted, giving her a 2-1 lead.
Sabalenka turned toward her box and shouted in frustration but then regained her composure, breaking back to level the match at 3-3.
She was broken again at love, however, and Gauff then held serve twice to claim the title after a match that lasted two hours, 38 minutes.
"This will hurt so much, especially after such a tough two seeks playing great tennis in terrible conditions," three-time Grand Slam champion Sabalenka said as she stifled her sobs.
"Thank you my team for the support, I'm sorry for this terrible final.
"As always I will come back stronger.
"To Coco: you deserve it, you're a hard worker, a fighter."
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