Michael Heseltine had led the UK's largest independently owned publishing company since its foundation it in 1957.
He will continue to be chairman of the Haymarket Group holding company, but Rupert Heseltine will become responsible for Haymarket's publishing and events operation from January 2010.
Michael Heseltine made the announcement to staff in an email earlier this afternoon. The change is part of a wider restructuring of the senior management team at PRWeek's publisher.
In the email, Rupert Heseltine said: ‘I look forward to working closely with William and Kevin in developing the business and thank Michael for his trust and confidence in me. Michael has led us through recent difficult times and it will be an honour to assume this role for Haymarket Media Group.'
Haymarket's business development director Alan Kemp will also step down from his position in January, but will remain on the board.
Chairman and managing director of Haymarket Consumer Media and chairman of Haymarket Network, Kevin Costello, will assume the role of group managing director for all UK businesses, as well as India, Australia, Germany and Hong Kong.
William Pecover will remain the managing director of Haymarket's North and South American operations.
Both MDs will report to Rupert Heseltine.