The 25-year-old former Sale Sharks tight-head prop, who has won seven caps for England, joined Bath in 2014 and has played six times so far this term.
"It is the place for me. It is my home. I've loved the past few years here," Thomas told BBC Radio Bristol.
Thomas is currently out long term after suffering an anterior cruciate ligament injury in November.
"It wasn't a hard decision to make," Thomas added. "I've signed on for three years and I'm really excited."
Asked if he might play again this season, he replied: "It is a big doubt really.
"As a player you always like to push as much as you can but the physios always have your best interests at heart."
Bath are fourth in the Premiership after 13 league games this season and are at home to Brive in the quarter-finals of the European Challenge Cup after finishing top of their pool.
Injured front row Henry Thomas has signed a new three-year contract with Premiership club Bath.