Eugene Laverty is to partner former World Superbike champion Max Biaggi in the factory Aprilia team next season.
The 25-year-old has been confirmed as the replacement for Leon Camier.
Laverty, who was fourth on his debut season with Yamaha before the Japanese manufacturer pulled out of the series, has a two-year contract with Aprilia.
It was not at first clear whether Laverty would be team-mate to Biaggi on the official Aprilia squad or ride for a factory-supported satellite team.
The Toomebridge rider showed how fast he could be next season after setting the fastest time during a one-day test at Portimao in Portugal on his first outing on the Aprilia RSV4.
Laverty recently agreed a two-year deal to ride for Aprilia in the World Superbike series in 2012 and 2013.
"This was always going to be the best option," he said.
"It will be nice to share a garage with Max, knowing that I'll be on equal terms, and in with a chance of fighting for the world title.
"I've had a learning year in World Superbikes and now I want to win.
"The good testing session at Portimao definitely helped my cause and I'm in as strong a position as anyone."
Laverty had been linked with a number of World Superbike teams, and the Tech 3 Yamaha MotoGP team.
Laverty won both races at Monza earlier this year and also secured podiums at Silverstone and Magny-Cours.