The 27-year-old has scored 12 tries in 18 games for the Warriors, including a hat-trick in last weekend's Amlin Challenge Cup victory over Italian side Rovigo.
"Josh came to Warriors as a very raw player with a huge amount of ability and natural talent, particularly in attack," Worcester head coach Richard Hill said.
"His game needed refining to become a top Aviva Premiership player and credit to him he has worked exceptionally hard during his time here.
"Josh has become a very good defender and has filled some big boots since the departure of Miles Benjamin and Marcel Garvey last year.
"In attack he is now even more hungry for the ball and is a real predator.
"I think he has finally realised just how good a player he can be and I rate him as one of the best attacking wingers and in the top three in the country."