McLaren confirm Jenson Button & Fernando Alonso for 2015
Jenson Button's Formula 1 career will continue into a 16th season following McLaren's decision to retain him alongside new signing Fernando Alonso.
McLaren finally announced their line-up on Thursday after taking weeks to decide whether to keep Button, 34, or 2014 team-mate Kevin Magnussen, 22.
"I am very pleased to have been invited to do my bit," said Button. "In fact, I am absolutely raring to go."
Dane Magnussen remains with McLaren as test and reserve driver.
"Fernando and Jenson have started a combined total of precisely 500 grands prix between them - a mighty aggregate - and have won 47 of them," said McLaren chairman Ron Dennis.
"I can safely say, therefore, that we now have by an order of magnitude the best driver line-up of any current Formula 1 team."
Double world champion Alonso, 33, was signed weeks ago after being persuaded to leave Ferrari.
The Spaniard's capture is a big coup for McLaren, but they are unlikely to challenge world champions Mercedes in 2015.
The Surrey-based outfit are starting a new engine partnership with Honda, with whom they won four consecutive titles between 1988 and 1991, but to expect a sustained title bid in 2015 is overly optimistic.
"I am joining this project with enormous enthusiasm and determination, knowing that it may require some time to achieve the results we are aiming for, which is no problem for me," said Alonso.
He said he had received a number of "really tempting" offers but revealed McLaren had contacted him more than a year ago and asked him to return to the team he left at the end of 2007.
Magnussen, who made his F1 debut in 2014, had appeared favourite to get the drive alongside Alonso, but a late change of heart swung the decision back in Button's favour.
Button's new contract is said by insiders to be for one year with a further year as an option.
The Englishman, world champion in 2009, had admitted being unhappy about the delay but wanted to remain in F1 and test himself against Alonso, who is regarded by many as the best all-round driver in the world.
|McLaren's 2015 partnership|
|Fernando Alonso||Jenson Button|
Button's strong finish to 2014 helped convince McLaren to keep him, as was the fact he scored more than twice as many points as Magnussen, who finished second in Australia, the opening race of the season.
But there were those within McLaren who felt retaining the Dane was the better option, because of his youth and promise.
He was out-qualified by Button, whose F1 career began in 2000, 10 times in 19 races but insiders say McLaren's internal data suggests that he was marginally quicker over a single lap.
McLaren said Magnussen would remain an "important part of the team", with Button adding: "He is a very quick driver and a really nice guy."
BBC Sport asked McLaren boss Dennis to clarify the length of Alonso's contract and he said it was for three firm years with no facility by which it could be shortened.
Button added: "Like Fernando, I am certain that McLaren and Honda will achieve great things together and I feel sure that, working together, all of us will pull incredibly hard to create a brilliantly effective winning team."
The 2015 F1 grid
Mercedes - Lewis Hamilton and Nico Rosberg
Red Bull - Daniel Ricciardo and Daniil Kvyat
Williams - Felipe Massa and Valtteri Bottas
Ferrari - Sebastian Vettel and Kimi Raikkonen
McLaren - Fernando Alonso and Jenson Button
Force India - Nico Hulkenberg and Sergio Perez
Toro Rosso - Max Verstappen and Carlos Sainz Jr
Lotus - Pastor Maldonado and Romain Grosjean
Sauber - Felipe Nasr and Marcus Ericsson