Earlier this month, the group announced Mr Sorrell was under investigation over allegations of personal misconduct regarding company assets, which he rejected “unreservedly”.
On Saturday, Mr Sorrell said he was standing down as the “current disruption” was “putting too much unnecessary pressure on the business”.
Confirming his departure in a statement to the London Stock Exchange, WPP said: “The previously announced investigation into an allegation of misconduct against Sir Martin has concluded. The allegation did not involve amounts that are material.”
Roberto Quarta, who has been appointed executive chairman of WPP until the appointment of a new CEO, said: “Sir Martin has been the driving force behind the expansion of WPP to create the global leader in marketing services. 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 Sir Martin for his commitment to the business over more than three decades.”
Mr Sorrell said: “Obviously I am sad to leave WPP after 33 years. It has been a passion, focus and source of energy for so long. However, I believe it is in the best interests of the business if I step down now. I leave the company in very good hands, as the board knows.”