Rosberg joins Mercedes for 2010

The signing of the 24-year-old German has been expected ever since he confirmed in October that he would not remain with Williams for a fifth straight season.

"I am really happy to be a part of the Silver Arrows re-launch in 2010 as a driver for Mercedes," said Rosberg.

"No other brand in Formula 1 can look back on such a long and successful tradition in motor racing. I am very proud that I will now drive for the new Mercedes team and work with Ross Brawn.

"I am more motivated than ever and can hardly wait to start testing with the new Silver Arrow and for the first race of the new season at Bahrain in March."

Mercedes team principal Ross Brawn, who guided the squad to drivers' and constructors' titles this year under the guise of Brawn GP, believes that Rosberg is the ideal driver to join the team for 2010.

"We are delighted to welcome Nico to our Mercedes team and are very much looking forward to working with him," he said.

"Nico is a great talent, and with four years of experience in Formula 1, is a driver who will be able to make a valuable contribution to our team right from the outset.

"I had the pleasure of working with his father Keke during his Formula One career and it is great to see Nico following in his footsteps.

"2009 was Nico's best season in Formula 1 to date and we look forward to seeing his development continue with us at Mercedes next year."

Rosberg's team-mate is expected to be fellow German Nick Heidfeld, although no announcement has been made.