McLaren has announced that Williams technical director Sam Michael will join the team as sporting director from 2012.
Michael announced earlier this year that he would leave Williams following a dismal season for the Grove-based team, which has scored just five points after having endured its worst start to a season in Formula 1.
He was expected to work for Williams until the Korean Grand Prix before stepping down from his post, but Williams said he will leave after Singapore next week.
McLaren said Michael "will join the senior management team in addition to taking specific responsibility for the development and management of the team's trackside operations."
"I'm extremely excited to be joining Vodafone McLaren Mercedes," said Michael. "Being a racer my whole life, I know that McLaren is one of the all-time greats of Formula 1.
"I already know and respect many of the team's senior technical management figures, and becoming a member of that excellent working unit was one of the prime attractions of this new position.
"Equally, for some time I've closely observed and greatly admired both Lewis and Jenson as grade-one drivers, and therefore regard it as an enormous privilege to be able to work with both of them.
"I've spent 11 seasons with Williams, have many fond memories, and truly wish them all the best. In the near future, however, I will become 100 per cent focused on Vodafone McLaren Mercedes, and will be aiming to ensure that the team's famous rocket-red victory T-shirts will be seen many times over the coming years."
McLaren team boss Martin Whitmarsh added: "Speaking on behalf of everyone at Vodafone McLaren Mercedes, I'm very pleased to welcome Sam as an important senior addition to our race team.
"He'll bring a very valuable blend of experience and expertise to our pitwall, and will also enrich the technical management we provide for our drivers.
"I'm certain he'll work extremely well with our senior technical management team, which I firmly believe will now become the strongest in all of Formula 1."
Frank Williams said he was happy for Michael to have found another role to continue in Formula 1.
"I am delighted that Sam has found a new role that will enable him to continue to apply his energy, passion and experience to Formula 1," he said. "On behalf of everyone at Williams I wish him a successful move to his new team.
"I would also like to thank Sam for his help in enabling a swift and smooth transition to our new technical leadership. Mike Coughlan and Jason Somerville are settling in very well and the restructuring will be complete when Mark Gillan joins us as Chief Operations Engineer on 19 September."