WPP said today that US-based private equity firm Bain Capital would buy a 60% stake in Kantar, valuing the data analytics unit at about $4 billion in the proposed deal.
WPP is the owner of several global advertising agencies including JWT and Ogilvy.
It is in the middle of an overhaul following several profit warnings in 2017 and 2018 and turmoil linked to founder Martin Sorrell's abrupt departure over a complaint of misconduct, which he denied.
The sale to Bain Capital is aimed at steering the world's biggest advertising company back to growth.
WPP said proceeds on completion after tax and continuing investment in Kantar were expected to be about $3.1 billion, with the ad giant retaining about 60% of net proceeds to cut debt.
The balance of the proceeds would be returned to shareholders, WPP said.
Bain's interest in Kantar is the latest private equity deal to emerge in recent weeks.
Blackstone and Lego's founding family last month took Merlin Entertainments private in a $7.5 billion deal, in one of the biggest private equity deals in Europe in recent years.