The Bath-born front row will now be released from his contract to make the move to the Memorial Stadium ahead of next season.
Dean Ryan, Director of Rugby at Warriors, said: "We have recruited strongly at hooker with Argentina international Agustin Creevy joining us, the acquisition of former England Saxons player Chris Brooker and Nick Seymour coming into our Academy to compete for the No.2 shirt with Ed Shervington.
"We have been open and honest with Ollie over his future and he clearly wants to play as much first team rugby as possible. The move to Bristol, a club he knows well, should give him that opportunity at this stage in his career.
"Ollie will leave with our thanks for his commitment to Warriors and our best wishes for the future."