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
Protesters across Europe and the rest of the globe held women's marches following the inauguration of President Trump.
A look at some of the inventive, and sometimes humourous, placards displayed in women's marches across the UK.
Irish police have seized £32 million worth of cannabis hidden in farm machinery on board a ship docking in Dublin.