The global marketing colossus WPP named Mark Read, a longtime company executive, as its new leader on Monday as the advertising agency tries to rebound from the abrupt departure of its founder in April amid a personal misconduct investigation.

WPP, the world’s largest advertising group, said that Mr. Read, who had recently served as the chief operating officer, would become the company’s chief executive, effective immediately. Mr. Read, 51, replaces Martin Sorrell, the influential advertising executive who founded WPP in the 1980s and molded it in his image, but who quit this year while under investigation.

“Our industry is going through a period of structural change, not structural decline, and if we embrace that change we can look ahead to an exciting and successful future,” Mr. Read said in a statement released by WPP on Monday. “Our mission now is to release the full potential that exists within the company for the benefit of our clients, to accelerate our transformation and simplify our offering, and to position WPP for stronger growth.”