Although the highlight of Li's career remains her French Open title in 2011, this season has been by far her most consistent.
Apart from the clay-court stretch, she has reached at least the quarter-finals of every event she has played, including making a third grand slam final at the Australian Open in January.
The 31-year-old's overall level was simply too good for Kvitova, who made 29 unforced errors in 18 games to lose 6-4 6-2.
The hard-hitting Czech can be a very frustrating player to watch, with too many loose shots to go with the blistering winners, but a lot of her mistakes on Saturday could be attributed to the pressure Li put her under.
A combination of the Chinese player's excellent movement around the court and crisp hitting kept Kvitova on the run.
Having lost the first three games, two of which were on her serve, 2011 champion Kvitova did well to claw her way back to 4-4, but Li broke again before clinching the set.
The fourth seed then forged ahead in the fifth game of the second set and finished the match with a run of four games in a row.
The victory guarantees Li will leapfrog both Maria Sharapova - absent from the tournament with a shoulder problem - and Agnieszka Radwanska to finish the season as the world number three.
Additionally, Li will become the first Asian player ever to be ranked in the world's top three singles players, surpassing the previous high ranking of four that she shared with Japan's Kimiko Date-Krumm.
In her first WTA Championships final on Sunday, Li will play either world number one Serena Williams or Serbia's Jelena Jankovic.