The Pole, who went on a 37-match winning streak earlier in the year, won the French and U.S. Opens as well as titles at Doha, Indian Wells, Miami, Stuttgart, Rome and San Diego.
Swiatek was hot favourite to finish her year with the season-ending title at the WTA Finals in Fort Worth, Texas but was beaten 6-2 2-6 6-1 by Sabalenka in their semi-final.
"Not going to lie, I've been waiting for this moment," Swiatek told reporters. "It was pretty hard to see the finish line but still be fully motivated and ready for every match.
"This season has been so intense and I'm so proud of myself that I could play so well till the end. I'm happy it's done."
Swiatek's U.S. Open success saw her became the first woman to capture two Grand Slam titles in a season since Angelique Kerber won the Australian and U.S. Opens in 2016.
Sabalenka just outplayed her on the day, she said.
"In second set I wanted to kind of overpower her, but in the third I felt it's not my kind of game. I feel like I was playing too risky ... she used her chances and served really well," she added.
