Adrian Newey says he is looking forward to taking over as Red Bull Racing's chief technical officer.
Newey has decided to leave McLaren after eight years and will take up his new role at the end of February.
"I feel it is time for a change. I have thoroughly enjoyed my time at McLaren," said the 46-year-old Englishman.
McLaren described his exit as amicable but added that Newey was leaving "for a new challenge with a smaller team" under less pressure to win.
Newey helped Williams win four world titles McLaren win two. He will continue to work with McLaren until the end of January developing their new MP4-21.
He added: "Red Bull is a younger organisation, but I am excited by the opportunity to develop the car, team and facilities. I have been impressed by their plans."
McLaren said their split with Newey as "amicable and mutual".
But a spokeperson added: "The pressures of working for a front-running F1 team are intense and we have been aware for some time that Adrian was looking for a new challenge with a smaller team.
"For the past two years Adrian has been fully involved in the restructuring of McLaren's technical team.
"This team has already worked successfully together on the MP4-20 and continues to be fully focused on the MP4-21."