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".
The 27-year-old replaces Michael Schumacher at Mercedes, with the 43-year-old seven-times champion now likely to retire from Formula One for a second time.
Earlier, McLaren confirmed the signing Sergio Perez on a multi-year deal from next season as a replacement for Hamilton.
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.
"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."
Perez said: "I'm thrilled and delighted to have become a McLaren driver."
LEWIS HAMILTON FACTFILE
- 1985: Born Tewin, Hertfordshire, January 7.
- 1995: British cadet class and STP karting champion.
- 1996: Wins the Champions of the Future, Sky TV KartMasters and Five Nations karting series.
- 1998: Competing in junior Intercontinental A, is second in McLaren Mercedes Champions of the Future and fourth at the Italian Open. Confirms he will be supported by McLaren and Mercedes-Benz.
- 2006: Wins the GP2 Series.
- November 24 - Confirmed as race driver with McLaren for 2007.
- 2007: March 18 - Finishes third on Formula One debut at the Australian Grand Prix.
- April 15 - After finishing second in Malaysia, Hamilton is second in Bahrain to become the first driver in F1 history to finish on the podium in his first three races.
- May 13 - Another second in Spain makes Hamilton the youngest driver to hold the outright lead in the drivers' standings.
- June 10 - Claims first victory at the Canadian Grand Prix in Montreal after maiden pole.
- June 17 - Follows up with pole and win at United States Grand Prix in Indianapolis.
- July 21 - Suffers bruised ribs after a 175mph smash in qualifying for the European Grand Prix at the Nurburgring. Finishes ninth in following day's race.
- September 13 - McLaren are fined £49.2million and docked all points in the constructors' championship as a result of a spying scandal, but drivers' individual points are untouched.
- October 21 - Loses the title by a point to Kimi Raikkonen in Brazil where he only finishes seventh due to a gearbox problem early in the race.
- 2008: January 18 - Signs new five-year contract through to 2012, worth around £10million per year.
- June 8 - Crashes into the back of Raikkonen in the pit lane in the Canadian Grand Prix, incurring a 10-place grid penalty for following race in France.
- July 6 - Wins a rain-lashed British Grand Prix at Silverstone.
- September 7 - Wins Belgian Grand Prix at Spa, but is later dropped to third after being handed a retrospective 25-second drive-through penalty for cutting a chicane.
- November 2 - Becomes youngest world champion in F1 history after finishing fifth in the Brazilian Grand Prix.
- December 31 - Awarded an MBE in the New Year's Honours.
- 2009: March 10 - Collects MBE from the Queen at Buckingham Palace.
- April 2 - After finishing third in Australia, is excluded from the classification for lying to stewards in a post-race investigation into an incident with Toyota's Jarno Trulli.
- July 26 - Ends nine-month wait for a win with victory in Hungary.
- November 1 - After a further win in Singapore, finishes fifth in the championship.
- 2010: March 2 - On the eve of the new season, Hamilton splits with father Anthony as his manager.
- Wins three races, and although in with a slim chance of the title going into the final race, finishes fourth, 16 points adrift of Sebastian Vettel.
- 2011: March 14 - Hamilton signs new management in Simon Fuller's XIX Entertainment
- May 29 - Hamilton writes a letter of apology to FIA president Jean Todt after making reference to his skin colour for being hauled before the stewards after the Monaco Grand Prix in which he received two drive-through penalties.
- Wins two races, but endures an erratic season, finishing fifth and behind a team-mate in the standings for the first time in his single-seater career.
- 2012: Wins races in Canada, Hungary and Italy.
- September 28 - Signs a three-year contract with Mercedes from 2013.