Prop Bell, a member of the England squad for the so-called "Tour to Hell" Down Under in 1998, has agreed terms with the Recreation Ground club where he began his rugby as a schoolboy.
Bath, embroiled in a relegation fight at the bottom of the Zurich Premiership, pulled out of a similar deal with the 28-year-old last summer amid concerns over their rising wage bill.
But they are now understood to be ready to offer a two-year contract.
"Bath are the only other club to Pontypridd that I would want to play for and it is just too hard to turn down the opportunity," said Bell who was raised just outside Bath.
"I was given a deadline by when I had to give an answer so I had to go for it. The uncertainty in Welsh rugby did not help either."
Bell will see out the rest of the season at Pontypridd where he has formed a formidable front-row alongside Wales pair Gethin Jenkins and hooker Mefin Davies.
That trio provided the platform from which the Valleys club went on to win the Principality Cup and reach the final of the Parker Pen Shield last season.
A solid scrummager and destructive ball carrier, Bell has attracted attention from the Wales, England and Scotland coaches during his rise to prominence at Ponty though he has yet to be capped at international level.
"Coming to Pontypridd (from Sale in 2001) was probably the best move of my life and I am genuinely upset to leave," he said.
"I have been playing some of the best rugby of my career here and I will always be grateful to the club.
"But I feel I can improve even more by playing in the Zurich Premiership."
The departure of Bell, who is due to play in tonight's Principality Cup quarter-final against Cardiff at the Arms Park, will come as a major blow to Pontypridd who lost the race to sign fellow tight head Ben Evans earlier this week.