"At the age of 38, I believe it is time to put my time and energies into those areas and relationships that I have neglected," Thomas said on his Facebook page Sunday.
"That is why at this time I feel the most important thing I can do in my life is to reconnect with the three F's. Friends, Family, and Faith."
On Friday, general manager Peter Chiarelli said Thomas told the team he was thinking about sitting out a season.
A late bloomer who played in Finland before finally breaking into an NHL lineup at the age of 32, Thomas emerged as one of the league's top goalies when he won the Vezina Trophy in 2009. He won it again along with the playoff MVP in 2011 while leading Boston to the Stanley Cup championship.
But he is also an iconoclast who was known to wander far from the crease in games and occasionally leave his comfort zone off the ice as well. When the Bruins met U.S. President Barack Obama to celebrate their NHL title, Thomas skipped the White House visit and issued a political diatribe on his Facebook page as explanation.
Chiarelli said Friday that Thomas appeared tired after the championship season, when he played in 82 games, including every minute of the longest post-season in Bruins history. He got very little time off down the stretch this year after backup Tuukka Rask was injured at the beginning of March.
Chiarelli said Thomas expressed an interest in playing in the 2014 Olympics, which will be two months before he turns 40. But he is not certain to be picked for the U.S. team over Ryan Miller, Jonathan Quick, Jimmy Howard or another young American goaltender who might have emerged by then. Thomas was a member of the U.S. team in Vancouver, but he did not play on the squad that won the silver medal.
The Bruins are left with Rask and Anton Khudobin as their top two goaltenders for next season. Rask has long been projected as a rising star; he supplanted Thomas as the starter in 2009-10, but Thomas regained his position the next year and remained there.