A product of the Ulster Schools and Academy systems, Bowe broke into the Ulster team during the 2003/04 season. He has been an ever-present in the side since then, amassing over 80 appearances for Ulster and 10 Ireland caps and was a prolific try scorer in the Magners League.
His fine form of late, including a two-try salvo against Gloucester in the Heineken Cup last Sunday, earned him a call-up to the Ireland Six Nations squad but the Monaghan man has missed out on selection for Saturday week's opener against Italy and will instead play for Ireland 'A' against England Saxons next Friday.
Commenting on Bowe's departure from Ravenhill, Ulster Rugby CEO Michael Reid said: "We wish Tommy much success in this new phase of his career. We would have hoped for Tommy to remain with us and trust he remembers the door is always open for a return.
"While a player of Tommy's experience will be hard to replace it will give more regular opportunities for the fast emerging Mark McCrea and will allow us to bring other rising Academy stars into the squad," he added.
Meanwhile, Ospreys coach Lyn Jones expressed his satisfaction at completing the deal. He said: "We are delighted to be able to confirm the signing of Tommy Bowe, whose considerable talents will increase the options available to us behind the scrum.
"Although still only 23 years of age, he is a top quality player who has already enjoyed success with Ulster and has made an impact in international rugby.
"He has a very bright future in the game, and we're all delighted that this will be with the Ospreys. I'm sure that he will be prove to be just as popular at the Liberty Stadium as he is at Ravenhill."