The victory by World No.2 Gauff sets up a blockbuster championship match against World No.1 Aryna Sabalenka on Saturday.
Sabalenka is a three-time major champion and earned a shot at a fourth by ending Iga Swiatek's 26-match French Open winning streak.
Sabalenka's 7-6 (7-1) 4-6 6-0 win in Thursday's semi-finals prevents Swiatek from becoming the first woman to win four consecutive championships in Paris.
This will be just the second No.1 v. No.2 women's final at the French Open in the last 30 years.
It's also a rematch of the 2023 US Open final, in which Gauff beat Sabalenka to claim her first major trophy at age 19. Gauff was runner-up to Swiatek at Roland-Garros in 2022.
Boisson had sent shockwaves around Roland Garros by becoming the first wildcard to reach the semi-finals.
The 22-year-old from Dijon proved she could cut the mustard having knocked out third seed Jessica Pegula and sixth-ranked Mirra Andreeva. But Gauff subdued the Paris crowd with a composed victory in one hour and nine minutes.
"Congratulations to her on an incredible tournament," Gauff said, "but today just happened to be my day."
Earlier, Sabalenka's power had proved too much for Swiatek, who was looking to become the first female player in the Open era since 1968 to win four consecutive titles in Paris.
"Honestly, it feels incredible but I understand the job is not done yet. I'm just thrilled today with this win and the atmosphere," Sabalenka said.
"She's the toughest opponent, especially on clay, especially at Roland Garros. It was a tough match it was a tricky match but I managed."
Sabalenka, in her second French open semi-final and seeking her first title in Paris, powered into a 3-0 lead, twice breaking the Pole.
Swiatek, who has not won a title this year but reached the semi-finals dropping just one set in five matches, looked completely out of sorts.
With seven unforced errors in the first three games she was playing catchup from the start.
The Pole, who late last year accepted a one-month doping ban, struggled with her serve and had racked up two double faults by the fifth game.
She gradually, however, found her range and precision, countering Sabalenka's raw power with superb ball placement and levelled when her opponent double-faulted on break point.
The Belarusian was furious, angrily shouting to her team in the box, before overrunning her opponent in the tiebreak.
The pair traded breaks at the start of the second set before Swiatek earned another to level the match.
But Sabalenka again broke the 24-year-old world No.5 at the start of the third to take control and she powered through the decider as the Pole ran out of steam.
With AP
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