Mieres, 25, joined Exeter from Deportiva Francesa in October 2010 and it was during the 2011/12 season he made the No.10 shirt his own, scoring 240 points for the West Country club in all competitions and helping them challenge for an Aviva Premiership play-off berth.
"I know this move will be a big challenge for me," he said. "I don't know very many of the Worcester players and haven't been to the stadium lots of times, just when we play Warriors.
"But what I do know is that it is a big project at Warriors, the coaches have told me about the way forward and that is an exciting thing to be a part of. I am very excited by the new challenge.
"I'm very grateful to Rob Baxter and Exeter Chiefs for the opportunity that gave me over the last few seasons," he added.
"It is a great club with great supporters and very hard working and talented staff who deserve success.
"My focus is now on the rest of this season and giving I have, I want to have a strong finish with the Chiefs and a successful end of the season."