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.

Defence lawyer Brenda Weksler told a court in Las Vegas her client Michael Sandford, from Dorking, Surrey, was in a "delicate mental state".
Court papers said he had been on suicide watch at a detention centre.
Mr Sandford's mother Lynne, who was not in court for the hearing, wants him to return to the UK for psychiatric help.
Prosecutors allege Mr Sandford, 20, tried to grab a police officer's gun to shoot Republican presidential candidate Mr Trump at a campaign rally in Las Vegas on 18 June.
They also claim he practiced shooting at a gun range the previous day.
His trial has been scheduled for 3 October.
The Associated Press news agency said the meeting was also expected to include Ms Weksler and Ms Sandford's London lawyer Saimo Chahal.
US magistrate judge Cam Ferenbach said the meeting "might help in the resolution of the case in a way that benefits the defendant and the government", the agency reported.
Ms Sandford has said her son has autism, OCD, severe depression and would face up to 30 years in prison in the US.
She argues he should serve any sentence in a psychiatric hospital in the UK to receive help closer to his family.
He has denied charges of disrupting government business and official functions and being an illegal alien in possession of a gun.

European football's governing body introduced FFP 'break-even' rules in 2013, requiring clubs to balance their spending with their revenue.
PSG more than doubled the world record transfer fee when they spent 222m euros (£200m) to sign Neymar last month.
They have signed Kylian Mbappe on loan, and could pay £165.7m for him in 2018.
PSG have been owned by the Gulf state of Qatar, via its Qatar Sports Investments fund, since 2011.
The French club made made a profit of 10m euros (£9.2m) on revenue of 520.9m euros (£389.6m at the time of conversion) in the 2015-16 financial year, according to the most recent figures published by Deloitte.
The six-time French champions have failed to meet FFP rules before - receiving a fine, a spending cap and only being allowed to register 21 players for the Champions League in 2014.
Uefa's FFP regulations were approved in 2010 and the first assessments began the following year.
The 'break-even' element states clubs can spend 30m euros more than they earn over a three-year period.
A Uefa statement said the investigation into PSG would "focus on the compliance of the club with the break-even requirement, particularly in light of its recent transfer activity".
It added: "In the coming months, the investigatory chamber of the Uefa club financial control body will regularly meet in order to carefully evaluate all documentation pertaining to this case.
"Uefa considers financial fair play to be a crucial governance mechanism which aims to ensure the financial sustainability of European club football."
Injured front row Henry Thomas has signed a new three-year contract with Premiership club Bath.
[NEXT_CONCEPT]
The mother of a Briton accused of trying to shoot and kill Donald Trump has been given permission to visit him in custody in the United States.
[NEXT_CONCEPT]
Uefa has opened a formal investigation into Paris St-Germain as part of its "ongoing monitoring" of clubs under financial fair play (FFP) regulations.