Jenson Button has signed to drive alongside Lewis Hamilton in an all-English line-up at McLaren next season.
The world champion's move was announced on Wednesday following news that former world champion Kimi Raikkonen will not race in F1 next year.
Button described leaving the Brawn team for whom he won the title as a "difficult decision".
But the 29-year-old added: "Life is about challenges. Most important of all, it's about challenging yourself."
In new team-mate Hamilton, Button will be competing against a man many regard as the fastest driver in F1.
And while the move leaves McLaren with one of the most exciting driver line-ups, Button is facing arguably the toughest challenge of his career.
He added: "Although I won the World Championship with Brawn GP last year, and I'll never forget that, I was always adamant that I wanted to continue to set myself fresh challenges.
Lewis is a wonderfully gifted driver who has earned the respect of every Formula 1 driver - I'm sure there's plenty that we can learn from each other
"That's why I've decided to join Vodafone McLaren Mercedes. You can't help but be affected by this team's phenomenal history.
"McLaren is one of the greats of world sport, and its achievements and list of past champions read like a Who's Who of Formula 1 - Emerson Fittipaldi, James Hunt, Niki Lauda, Alain Prost, Ayrton Senna, Mika Hakkinen and of course my new team-mate Lewis Hamilton.
"I've followed the McLaren team ever since I was a small boy, and it feels unbelievable to finally be a part of it.
"When I visited the McLaren Technology Centre earlier this month, it wasn't simply the technical resources and the incredible standards of excellence that impressed me.
"No, I was equally struck by the ambition, the motivation and the winning spirit that flow through everybody there. And then there's the team's epic history: put it this way, the trophy cabinets seem to stretch for miles.
"From a personal point of view, it's also a great pleasure to be joining a fellow British world champion.
"Lewis has achieved an incredible level of success in a very short period of time, and he's a wonderfully gifted driver who has earned the respect of every Formula 1 driver.
"I'm sure there's plenty that we can learn from each other, and I'm really looking forward to using our combined knowledge to push the team forward."
Button paid tribute to Brawn, whose participation in F1 last year was only confirmed with a month to go before the start of the season following Honda's decision to quit F1.
"I want to say that the 2009 season will always have a special place in my memory, and I'm absolutely sure that everybody at Brawn GP who worked so hard to achieve our world championship successes feels exactly the same way about it," he said.
Button's switch means McLaren will be fielding the last two world champions in the same team, with Hamilton having won the drivers' title in 2008.
Jenson Button's career in F1
"It has always been our policy to employ the two very best possible drivers," said McLaren team principal Martin Whitmarsh.
"In Jenson and Lewis, we feel we not only have the fastest pairing on the 2010 grid but also the two most complete, professional and dedicated drivers in Formula One.
"I want to make clear that Jenson's decision to join us was in no way motivated by money. We'll be paying him no more than he could be getting elsewhere."
Hamilton wished his former team-mate Heikki Kovalainen the best for the future, describing the Finn as "one of the nicest human beings I've ever met".
Hamilton added: "It's fantastic news that Jenson has decided to join McLaren - and I'm looking forward to working with him and our engineers to make sure we kick off the 2010 season with a car that's competitive enough to win the world championship
"I already know Jenson, and we get on very well together.
"We both really want our team to succeed. Although we'll be pushing each other hard, I'm sure we'll very quickly establish a great working relationship.
"He's an exceptional driver: very controlled and very smooth, and he has a real depth of knowledge and experience. I think we'll complement each other very well, and our collaboration will make the team stronger as a result. I believe we can pull together to make McLaren the best team on the grid."
Button's former team Brawn, who have been taken over by Mercedes, made Button an offer, but he did not consider it acceptable.
After a poor start to the 2009 season, McLaren came back strongly in the second half of the year, while Brawn, after dominating the first third of the season, slipped back in competitiveness as the year went on.
Button move a mistake - Stewart
McLaren will be the first team to start a season with the last two world champions as their drivers.
And it will be the first pairing of two British world champions since Graham Hill joined Jim Clark at Lotus in 1968.
Brawn emerged from the ashes of the former Honda team, after the Japanese company pulled out of F1 last winter.
Button took a pay cut last winter to help secure the team's future and they went on to win the world championship together in Brawn's debut season.
Now renamed Mercedes Grand Prix, the team have already signed the German Nico Rosberg as one of their drivers.
His fellow German Nick Heidfeld is the favourite for the second seat.
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