Hooper, who represented England at under-21s level, insist he will remain fully committed to the Tykes cause until the end of the season - despite his departure.
"I am honoured to have the opportunity to join a club with the heritage of Bath," he said.
"I am extremely excited about challenging for a place in the team. But that is for next season - and my focus, for now, will remain on helping Leeds remain in the Guinness Premiership.
"I have worked with some great players and coaches during my time at Headingley and I am sure the club will continue to grow in the coming years.
"However, I am originally from the south-west, and the opportunity to move closer to home was a factor in my decision.
"My wife and I are expecting the arrival of our first child very soon, and this is an exciting time to start our new life down in Bath."
Bath head coach Steve Meehan added: "It will be good to have a player with the Premiership experience that he has - and I hope he will bring a fresh set of ideas.
"He is the type of individual that I am confident will help Bath develop further.
"He has shown his character his strength of character through both good and bad at Leeds, and we are looking forward to teaming up with him in the pre-season."