Ogilvy & Mather veteran John Seifert has succeeded Miles Young as Worldwide CEO, effective immediately. On Sept. 1, Mr. Seifert will also take on Mr. Young's role as global chairman.

After September, Mr. Young will take on a non-executive position, continuing to work with key global clients for Ogilvy & Mather and parent company WPP. He will also become warden of his alma mater, New College at Oxford University.

Mr. Seifert, who has been with the agency for 37 years, will retain his most recent role as Chairman and CEO of Ogilvy & Mather North America. He will work closely with Global Chief Creative Officer Tham Khai Meng, who is being named Co-Chairman of the Ogilvy & Mather Worldwide Board. On Sept. 1, Mr. Seifert will assume responsibility for the board from Mr. Young as Worldwide Chairman.

Representatives from Ogilvy & Mather were not available for comment.

Additionally, Paul Heath, Chairman and CEO of Ogilvy & Mather Asia-Pacific, and Paul O'Donnell, Chairman-CEO of Ogilvy & Mather Europe, Middle East, and Africa, will take on the expanded roles of worldwide executive directors for global business development and agency transformation, respectively.