Sabalenka's power was too much for the defending champion, who was looking to become the first female player in the Open era since 1968 to win four consecutive titles in Paris.
The top seed will play either France's wildcard Lois Boisson or second seed American Coco Gauff in Saturday's showcase match.
"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. "It could not be more perfect than that," Sabalenka said of her third set performance.
"I'm super proud right now, I'm glad I found my serve (again in the third set)."Â
