The 28-year-old made 35 appearances in the Magners League, including nine last season, but will now try his hand in the Guinness Premiership.
Ironically, Powell has decided to join a team who were beaten by the Blues in the semi-finals of last season's Amlin Challenge Cup - a tournament Dai Young's men went on to win thanks to an historic victory over Toulon in Marseilles.
Powell had been linked with a big-money move to France with Agen and a cross-code switch to the Crusaders but he has instead decided to swap Wales for England as he attempts to keep his international prospects alive.
"My decision was a pure rugby decision," said Powell, who has signed an initial one-year contract with the Adams Park club.
"After all the talk and speculation about where I will be playing, all I want to do now is get my head down, improve as a player and hopefully, if selected, play in the World Cup next year for my country.
"To do that I need to be playing well for my club and I think with the coaching team and setup here at Wasps, I will have the perfect opportunity to do that.
"I know Shaun Edwards well of course from my time with the Welsh team, and I took little persuading once I met with Tony Hanks and Trevor Woodman about how serious this team is about success and winning."
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