The 33-year-old No 8 has signed from French giants Toulon having also previously represented Aviva Premiership side Northampton Saints.
Manoa’s arrival has seen Blues head coach John Mulvihill add further international quality to his squad ahead of the upcoming season.
“I’m really looking forward to the next chapter and getting stuck in at Cardiff Blues,” said Manoa, who will join his USA team-mate Blaine Scully in the Welsh capital.
“They had great season last year, winning the European Challenge Cup and sealing a return to the Champions Cup, so it is a great time to join.
“I have spoken to both John and Blaine at length and have heard nothing but good things about the set-up at Cardiff Blues, the city itself, and the region.
“My family is the most important thing to me and hearing about how well players and their families are taken care of at the Blues was a big lure. If they are happy, I am happy and can be at my best.
“So I’m really excited about moving them over to Cardiff and then meeting my new team-mates, competing for places, and contributing to the Blues as they look to build on the success of last season.”
Following the signings of Dmitri Arhip and Jason Harries, plus a season-long loan to bring Rory Thornton to the Welsh capital, Manoa has handed the Blues another major boost.
Manoa made more than 50 appearances for Toulon. In his time with Saints, he won both the Aviva Premiership and European Challenge Cup in 2014.
Standing at 6ft 7ins and tipping the scales at 20 stone, Manoa brings a formidable physical presence to the Blues’ pack and is able to play both in the back-row and also at lock.
Mulvihill said: “This is another significant signal of intent as we build towards the new season and a return to the European Champions Cup.
“Samu is a big, physical man, who will compete with Nick Williams for the No 8 jersey and bring an abundance of experience to our pack.
“It is important we take some of the work-load off Nick and Samu will work in tandem with him, ensuing we have a real physical presence for the full 80 minutes.
“We’re now looking forward to getting him over here and seeing him in a Cardiff Blues jersey at the Arms Park.”
