Toni Elias, the 2010 Moto2 world champion, will rejoin MotoGP in place of Claudio Corti at Forward Racing from the Aragon Grand Prix.
Elias has already made an appearance this season when he replaced an injured Karel Abraham on the Cardion Honda at Indianapolis.
He made his MotoGP debut in 2005 and scored his first and only MotoGP career win at the '06 Portuguese GP, denying Valentino Rossi victory by 0.002 seconds on his Gresini Honda.
A season in Moto2 in 2010 was the most successful year in his motorcycle racing career, as he won the series' inaugural world championship.
"I can't be happier to be back racing in MotoGP," said Elias, whose last full season in the top class was with LCR in 2011.
"This year I was already on track at Indianapolis but only for one race.
"With Forward I get the chance to finish the season.
"The goal is to work hard and enjoy the ride, the results will come. I am very motivated and enthusiastic."
Elias's deal confirms that Forward - which missed Indianapolis due to financial issues related to team owner Giovanni Cuzari's arrest - will complete the 2015 season.
Corti had stood in at the team when original rider Stefan Bradl was first injured and then left for Aprilia amid Forward's troubles.
The team statement thanked Corti, who had previously been part of Forward's line-up in Moto2 in 2010 and MotoGP in '13, adding: "We would like to praise him for his professionalism, especially when facing such a difficult situation; we wish him the best for his future and his career".
Forward's other rider Loris Baz gave the team its best result of 2015 when he finished fourth in last weekend's rain-affected San Marino GP at Misano.