O'Sullivan said: "Tommy will be a great signing for the Ospreys and make a huge impact. He is extremely talented, enthusiastic and on top of his game.
"He will be a huge hit with the Ospreys fans and they now have two world class wingers in Tommy and Shane. They will certainly deliver exciting rugby this season."
O'Sullivan handed the former Ulster winger his Test debut against USA in 2004. Bowe responded with a second half try but injuries and a loss of in form halted his progress. And he has been forced to wait until this year's RBS Six Nations and summer tour to New Zealand and Australia to finally cement his place as first-choice in the Ireland set-up.
O'Sullivan added: "Tommy got picked for the first time at a very young age and like a lot of players in international rugby, he hit a lull after that. It's a common problem but he has bounced back now and his form for Ireland this year has been nothing short of outstanding."