He has been with the Ogilvy group for 16 years and leaves with effect from 30 September 2009.
O’Donnell is currently chairman of OgilvyOne in Europe and Vice Chairman, Ogilvy Europe, responsible for cross-discipline development of digital. O’Donnell will be responsible for the UK with immediate effect and will work with Leih on a smooth transition over the summer months.
He has worked with Ogilvy in Asia/Pacific, Latin America and Europe and has been based in the UK for the past decade.
Rory Sutherland will continue as Group vice chairman.
Leih joined WPP-owned Ogilvy Group UK in June 2005 from the position of group managing director at Ogilvy Africa.
A new chief executive for Ogilvy Advertising is being recruited and in the meantime, Will Awdry, currently a Creative Partner, will take on the role of Acting MD of the agency. The rest of the Group structure remains unchanged.
Shelly Lazarus, Chairman of Ogilvy & Mather Worldwide, says: “Gary has made a huge contribution to our company, and we’re sorry to see him go. He made a remarkable difference to the London office. If Ogilvy Group UK is a leader in integrated marketing services today, it was Gary’s energy and optimism that sparked the renaissance. We will miss him.”