Kenyon, who is widely viewed as being responsible for taking Manchester United to the top of football's commercial tree as the world's richest club, has agreed a switch to newly rich Chelsea.
The acquisition of Kenyon comes after Chelsea's new Russian billionaire owner Roman Abramovich has spent over £110million on new players for the club.
United have named David Gill as their new chief executive after breaking news of Kenyon's resignation to the stock exchange.
Gill, previously managing director at Old Trafford, will move into the role relinquished by Kenyon "with immediate effect".
Kenyon, 49, has accepted the job of chief executive officer of the "Chelsea group of companies" and has been put on gardening leave by United.
A United statement read: "The board of Manchester United plc is delighted to announce the appointment of David Gill as its new chief executive with immediate effect, to replace Peter Kenyon who has resigned today.
"Mr Kenyon will now go on garden leave in accordance with the terms of his contract."
In a shock move, Manchester United chief executive Peter Kenyon has quit his post to take up the corresponding position at English Premier League rivals Chelsea.
