But those involved with the company are likely to be scratching their heads this morning as to what he is alleged to have done.
Sorrell will "be treated as having retired on leaving WPP", with share awards pro-rated and vesting over the next five years, the FTSE 100 firm said.
Sorrell's prognostications on the business climate have always been sought after, and his vast pay and colourful private life have kept him in the headlines for two decades.
WPP said that the announcement concludes the investigation, noting that "the allegation did not involve amounts that are material".
In a statement also released last night, Sorrell said: "The current disruption we are experiencing is simply putting too much unnecessary pressure on the business".
And last month amidst slowing down of revenues and income and the growing clout of the FANGS - the board commenced an investigation charging Sorrell with personal misconduct and misuse of the company's assets.
Having denied the unspecified allegation made against him by a whistleblower, Sir Martin's decision to resign will inevitably spark speculation about the nature of the claims made against him. Frankly, he feels the whole process has not been handled well and has been very unpleasant.
Some multinational advertisers, including P&G, which owns Ariel and Gillette, have signalled their intention to take more of their marketing services activity in-house, reducing the lucrative work for which they are charged by external agencies.
The chairman of WPP, Roberto Quarta, will oversee the agency until a new CEO is appointed.
"This allegation is being investigated by a law firm".
Sorrell turned WPP from a maker of wire baskets called Wire and Plastic Products into one of the major global advertising giants.
The company said Sorrell would be available to assist with the transition, and the man synonymous with the British marketing group told the staff they would come through this hard time.
For years, the board supported his outsize pay packages amid shareholder complaints because he delivered. The agreement included a £3.25 million Georgian townhouse in Central London.
Beyond its marketing services and PR operations - of which WPP's global media agency powerhouses such as MediaCom have been the engine of its profits and revenue growth - DeGroote says there is a "treasure trove of hidden value" on WPP's balance sheet worth billions of pounds that is not reflected in its core profits. "During this time, the company has been successful because it has valued and nurtured outstanding talent at every level - within and well beyond our leadership teams. On behalf of the board I would like to recognise these achievements and thank Sorrell for his commitment to the business over more than three decades", Quarta said.