|The sun has set on Rosberg's Williams career [GALLO/GETTY]
Mercedes GP have signed Nico Rosberg as the first replacement for Rubens Barrichello and world champion Jenson Button, who raced under the Brawn name last season.
Rosberg has spent the last four years competing for Williams, where Brazilian Barrichello has taken his place.
Yet to win a race in 70 starts, the 24-year-old son of Finland's 1982 champion Keke finished seventh overall in 2009.
His best finish is second place in Singapore the year before.
Mercedes took over the British-based Brawn team last week, renaming it.
Brawn, who emerged from the remains of the Honda team, won both titles in their debut season but Britain's champ Button has joined compatriot Lewis Hamilton at McLaren to join Barrichello at the exit.
"I am really happy to be a part of the Silver Arrows re-launch in 2010 as a driver for Mercedes," Rosberg said in a statement on Monday.
"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 on 14 March."
Team principal Ross Brawn added: "Nico is a great talent and with four years of experience in Formula One 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."
Mercedes have yet to name their second driver, amid media speculation that seven-times world champion Michael Schumacher could be tempted out of retirement at the age of 41.
Team chief Ross Brawn dismissed speculation that it would be retired seven-time champion Schumacher, telling the Bild newspaper on Monday that the German had no plans for a comeback.
Finland's 2007 champion Kimi Raikkonen, who has announced plans to take a year out after leaving Ferrari, could be another option while Germany's Nick Heidfeld is available and seen as a safe pair of hands.