Reports surfaced Friday that Thomas was considering taking a break from the game, and Bruins General Manager Peter Chiarelli confirmed the netminder was considering not playing in the 2012-13 season.
Thomas made it official was a Facebook post Sunday.
"From the earliest age I can remember, I've wanted to be a hockey player," he wrote. "I've been blessed in my life to not only be able to live that dream, but to achieve more than I ever thought possible.
"The single-minded focus that is necessary to accomplish a dream of this magnitude entails (by necessity) sacrifice in other areas and relationships in life.
"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. 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.
"This is what I plan on doing over the course of the next year."