Sorrell has headed the advertising giant for three decades.
The world’s largest ad company is identifying internal and external chief executive officer candidates, the chairman, Roberto Quarta, said in the annual report on Friday.
Mr Sorrell, Britain’s highest-paid chief executive, is receiving compensation valued at £70.4m (€90.5m) for 2015, according to the report.
Most of the sum comes from a controversial incentive plan, which has triggered protests from shareholders and public interest groups.
While Mr Sorrell, 71, hasn’t announced any plans to step down, it will be a challenge to find a leader who can bring similar visibility to WPP, as it seeks to outpace rivals, Publicis Groupe, Omnicom Group, and Havas.
Mr Sorrell is known for more than his marketing know-how, weekly appearing on television, and attending events such as the World Economic Forum, to comment on everything from economics to politics and fashion.
He popularised terms such as ‘bathtub-shaped’ to describe economic recoveries, and ‘gray swans’ to foreshadow trouble.
“He has a legacy almost on the level of Steve Jobs, with what he’s done to the world of advertising, with Publicis and Havas having always followed,” said Cyrus Mewawalla, a media analyst at CM Research, in London.
“Sorrell has brought traditional advertising into the digital age,” he said.
Mr Sorrell bought wire-shopping-basket-maker, Wire & Plastic Products, in 1985, and used it as a shell to build an advertising conglomerate, which today operates in 100 countries and boasts a valuation of £21bn.
Although he’s led the company from the start, he has faced calls, from investors, in recent years, to outline succession plans.
“Shareowners should have no doubt that we already have a strong pool of internal and external candidates to draw from,” Mr Quarta said in the annual report.
“I, and the other independent members of the board, will continue to focus on this in 2016, and beyond,” he said.
Under Mr Sorrell’s leadership, WPP acquired ad agencies, Ogilvy & Mather, Grey, and Young & Rubicam, and his companies have crafted campaigns such as the Dove ‘Real Beauty’ commercials.
Mr Mewawalla said WPP’s goal should be a successful succession, like the one undertaken at Microsoft, where Satya Nadella took over from Steve Ballmer, in 2014.
“Nadella is in charge and everyone knows that and he’s gotten no overhang from Ballmer, or former CEO Bill Gates,” Mr Mewawalla said.