He announced on the field at Fenway Park before a victory parade Wednesday that he was declining a contract option that would have enabled him to become a free agent.
Price, 33, who also said in September that he didn't plan on opting out of his deal for 2019, said he came to Boston to win, and that's what the Red Sox did.
He will earn $127 million over the next four years under the seven-year, $217 million contract that he signed with Boston before the 2016 season. He has gone 31-19 with a 3.74 ERA in three seasons with the Red Sox.
After losing the first nine playoff decisions of his career, Price was the winning pitcher in the AL Championship Series clincher against Houston. He then won his first career World Series start, Game 2 against Los Angeles. He got two outs in Boston's 18-inning Game 3 loss, then started on three days' rest and delivered seven innings of three-hit ball to help eliminate the Dodgers.
In all, Price was 3-1 with a 3.46 ERA this postseason and 2-0 with a 1.98 ERA in two starts and one relief appearance against the Dodgers.
"He joined us because he wanted to be part of what we had, and that is something that's been on his back," Red Sox president of baseball operations Dave Dombrowski said after the clincher. "You know he can do it, but it's nice to get it off his back."
The Associated Press contributed to this report.