Tommy, 31, boasts plenty of experience having represented the Cook Islands at international level.
He enjoyed a lengthy spell at Glasgow and also masterminded Worcester's promotion from National League One a year ago.
The New Zealand-born player's chances were restricted in the Premiership last season with the Warriors preferring James Brown in the No 10 shirt.
But Tommy, who has joined on a two-year deal, still made 15 league appearances for the Sixways outfit and Hill believes he will fit in straight away when he arrives at the club on July 1.
Hill said: "I like the way Tommy plays, he is like a free spirit.
"I don't think he was suited to the way Worcester played last season. He prefers not to stick to a rigid game plan and enjoys freedom to play what he sees. This philosophy and skill will fit in exactly with the Bristol playing philosophy.
"He wants to play for two more years, he has plenty of experience and knows the game inside out. Tommy wants to play at Bristol and enjoy his rugby."
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