Thomas Cook chief executive Manny Fontenla-Novoa hs resigned after the holiday company issued three profit warnings in a year.
Sam Weihagen, his deputy, will be interim chief executive while a successor is found
Thomas Cook said that Fontenla-Novoa had left the company "with immediate effect".
In a brief statement Fontenla-Novoa, who had run the group since June 2007, said: "Thomas Cook and its people have a sound heritage and I have been proud to have been part of the company."
It is been a turbulent period for the holiday industry with the ash cloud crisis and unrest in North Africa and the Middle East taking their toll as well as economic woes across the globe.