The team announced the extension Friday. Terms were not disclosed, but the deal reportedly brings Thomas, who made $1.1 million this season, in line with some of the best-paid goaltenders in the league.
The 34-year-old Thomas, who could have become an unrestricted free agent after the season, leads the league with a 2.11 goals-against average and a .932 save percentage. He has established career highs this season with 33 wins while leading Boston to its first 50-win season since 1992-93.
"Look at where we came from," he said after Thursday night's victory over Ottawa. "Not making the playoffs two years ago, then last year doing a great job at the end of the year to get into the playoffs and then this year taking the next step. It's huge for this team."
A two-time All-Star, Thomas was given the Bruins' Seventh Player Award in 2006 and again in '07 for exceeding expectations. This year's award went to David Krejci on Thursday, and Thomas conceded that the days of him being honored for "exceeding expectations" are in the past.
"I guess that's a good thing," he said.
Thomas was a four-year starter for the University of Vermont who was signed by Boston as a free agent in 2001.