Klien lost his Red Bull drive to Mark Webber

Klien was dropped by Red Bull towards the end of last season. He replaces Anthony Davidson, now at Super Aguri.

The Austrian joins as test and reserve driver, behind Jenson Button and Rubens Barrichello, while Rossiter steps up to the role of an official test driver.

Sporting director Gil de Ferran said: "Christian's experience should prove extremely valuable to us."

Klien, 23, worked his way up through karting, Formula BMW, Formula Renault and the Formula 3 Euroseries to F1, where he has raced in 46 Grands Prix since his 2004 debut.

De Ferran said: "We expect Christian to play an important role in the development of the RA107 and we look forward to working very closely with him in the winter, together with James."

He added: "On behalf of everyone at Honda Racing, I would like to offer our congratulations to Anthony on his new role at Super Aguri.

"We are absolutely delighted that he has achieved his long-standing ambition of a F1 race drive, a role that he certainly deserves."

Klien said: "I am very proud to be joining Honda Racing.

"This is a fantastic opportunity for me to work with one of the top manufacturers in F1 and alongside two of the best race drivers.

"I am very much looking forward to driving the car for the first time when winter testing begins."