Alan Brydon, the CIA Medianetwork managing director, is to leave the company following a restructure. He will not be replaced.
Brydon has long been expected to exit CIA, which has experienced a difficult couple of years culminating in the loss of its biggest client, BT.
His departure follows the appointment last year of David Wheldon, the former Coca Cola marketing director, as chief executive officer.
The restructure at CIA also sees deputy vice chairman, Tony Kenyon, move to a group role.