Tom Alexander will step down as CEO at joint Orange and T-Mobile firm Everything Everywhere at the end of August 2011 for personal reasons.
Alexander became CEO at Orange UK in 2008, before becoming CEO of Everything Everywhere when Orange UK and T-Mobile UK merged in 2010. He will step down on 31 August 2011, but will continue to advise the company.
In a statement, the company said Alexander had resigned for "personal reasons and to pursue other interests".
"There is never an easy time to leave a company that you care deeply for, but for personal reasons, I feel now is a good moment to step back," he said.
Alexander added he is proud of the company's rapid integration and company-wide restructuring.
Successor from France Telecom
Olaf Swantee, currently France Telecom's executive vice-president for operations in Europe, will replace Alexander from 1 September 2011.
Everything Everywhere said Swantee has successfully transformed Orange throughout Europe and has been on the board of the company since its inception.
Swantee has previously worked in the IT industry for 17 years for companies including HP and Compaq.
Tim Höttges, chairman of Everything Everywhere's board and chief financial officer of Deutsche Telekom, said: "Olaf Swantee has a deep knowledge of Everything Everywhere's business and has been a director on the board of the company since its very beginning. He is ideally placed to provide both continuity and progression."