(Reuters) - WPP named former BT chief Philip Jansen as its new chair on Tuesday, succeeding Roberto Quarta at the world's largest advertising company.

Jansen will join WPP's board in September and replace Quarta, who has been in the role since 2015, on Jan. 1.

The appointment comes at a time when WPP, which owns the Ogilvy and GroupM agencies, became a clear laggard among global ad companies with an organic revenue drop in the first quarter, hurt by less spending from tech clients, a downturn in China and the loss of business from Pfizer.

"(Quarta) has helped to steer the company through significant challenges including the Covid-19 pandemic, overseen the restructuring of our portfolio to return WPP to financial stability, and guided the fundamental reshaping of our offer to meet the needs of modern marketing," WPP CEO Mark Read said.

Jansen left BT earlier this year.

(Reporting by Prerna Bedi and Yadarisa Shabong in Bengaluru; Editing by Eileen Soreng)