Matavesi, who previously played for Exeter Chiefs until his move to the Top 14 in 2011, will move to Sixways from the start of next season following the completion of talks.
The Cornwall-born 21-year-old, who can play across the back line and has featured regularly at inside centre for Racing Metro, has already earned five international caps for his country scoring 12 points with the boot.
Head Coach Richard Hill said: "We are very pleased that we can confirm the news that Josh will be joining the Warriors.
"We needed two good strong inside centres now we have released Dale Rasmussen and Sione Tu'ipulotu. Ravai Fatiaki has been fantastic the last six months with us and has really good potential. When you add that to the signing of Josh, we are pleased with our midfield options.
"Josh is a player we've been watching closely and he excites us with the way he plays. We already have some players within our squad who know him well from his Exeter days and Cornish connections.
"He has had a great experience at Racing Metro, where he has played Heineken Cup rugby, and he is excited about his move to Sixways. He is somebody who is an attacking player, who plays with flair and will look to unlock defences, which is what we need to add to our game.
"Josh takes ball to the line, is good at offloading out of contact and as a Fijian he loves to tackle hard. Phil Larder is looking forward to working with him and integrating him into our systems.
"Josh also gives us a kicking option in midfield or if he operates at full back or fly half. He gives us plenty of options and we are excited about the prospect of seeing him in action for the Warriors."
Matavesi added: "I'm very pleased to be coming back to the Aviva Premiership and show how much I have improved as a player. This is a big opportunity for me at Sixways and one I plan to take with both hands."
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