Finland's Kovalainen left Renault after one season

The 26-year-old, who scored 30 points in his maiden F1 season with Renault, has signed a "long-term contract".

"I think Lewis and Heikki will be a formidable combination," said McLaren chief executive Martin Whitmarsh. "I am confident they'll work well together."

Spaniard Pedro de la Rosa, who had been vying with Kovalainen for a race seat, will remain as test driver.

McLaren were left looking for a second driver after Fernando Alonso left the team to return to Renault following a turbulent season in which he fell out with boss Ron Dennis and Hamilton.

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Kamonte

Norbert Haug, vice-president of McLaren's engine partner Mercedes, said he was confident Hamilton and Kovalainen would form a strong partnership.

"Everybody in the team is looking forward to a very fruitful co-operation," he said.

"Lewis and Heikki will form one of the youngest driver line-ups, and I am convinced that both will be very strong and at the same time co-operative competitors."

Kovalainen - who has written a regular column for the BBC Sport website this year - had already been linked with a move to McLaren when it was confirmed earlier in December that Alonso and Nelson Piquet Jr would fill the race seats at Renault next season.

By joining McLaren, Kovalainen follows in the footsteps of fellow Finns Keke Rosberg, Mika Hakkinen and Kimi Raikkonen.

We will do everything we can to ensure that our championship challenge is as strong and focused as possible

Lewis Hamilton

"It's an honour for me to follow in Mika and Kimi's footsteps," he said.

"I haven't really spent a lot of time with Lewis so far but from what I know I think we will work well together and do our best for the team."

Hamilton, 22, welcomed Kovalainen's arrival.

"I am really looking forward to 2008 and working with Heikki as my team-mate," said the Briton, who finished second in last season's championship.

"Together with the team we will do everything we can to ensure that our championship challenge is as strong and focused as possible."