He took a United Kingdom manufacturer of wire baskets and built it into a worldwide provider of advertising, public relations and marketing services through a series of takeovers.
The question now for his successor, WPP's investors and its tens of thousands of clients is whether the £15bn group can survive the departure of its founder and the dramatic changes the internet is bringing to the traditional world of advertising.
Sir Martin's resignation will come 10 days after WPP said it had appointed independent counsel to investigate "an allegation of personal misconduct" against him. These are methods his successor can not hope to be allowed to employ.
He added in a letter sent to WPP staff: "As I look ahead, I see that the current disruption is simply putting too much unnecessary pressure on the business, our 200,000 people and their 500,000 or so dependents, and clients we serve in 112 countries".
Sky News has learnt that WPP, which owns a string of global advertising and media buying networks supplying numerous world's biggest companies, is preparing to announce Sir Martin's departure as soon as Saturday night.
Chairman Roberto Quarta will become executive chairman until a new chief executive is found, while Mark Read, a WPP digital executive, and Andrew Scott, chief operating officer, Europe, have been appointed as joint chief operating officers. "He wasn't widely liked but he was universally admired". The allegations do not involve amounts which are material to WPP as the holding company.
A spokesperson for WPP provided a statement, attributed to Sorrell which said, "Obviously I am sad to leave WPP after 33 years". Sorrell will be available to assist with the transition. Sorrell has denied the allegations, details of which have yet to publicly surface.
WPP said the investigation, which regarded financial impropriety, had concluded. "There is no other Sir Martin Sorrell in the world". "Most of my wealth, if not all of it, is and has been for the last 31 years tied up in the success of WPP". He will be treated as having retired on leaving WPP, as detailed in the Directors' Compensation Policy. Some of its biggest clients include Unilever and Procter & Gamble.