Lewis Hamilton will join Mercedes from next season on a three-year contract.
The decision to leave McLaren after a 14-year association with the team has been described by one source close to Hamilton as "the toughest of his career".
In a statement Hamilton said: "It is now time for me to take on a fresh challenge and I am very excited to begin a new chapter racing for the Mercedes Formula One Team. Mercedes-Benz has such an incredible heritage in motorsport, along with a passion for winning, which I share."
He added: "Together, we can grow and rise to this new challenge. I believe that I can help steer the Silver Arrows to the top and achieve our joint ambitions of winning the world championships."
More top news
David Cameron will stand down as Conservative leader ahead of the general election expected in 2020, Iain Duncan Smith said.
Delegates at the SNP spring conference have backed a move to allow all-female shortlists in the Scottish Parliament election next year.
Michael Clarke ended his one-day international career by leading Australia to a simple World Cup final win over New Zealand.