Head of strategic comms Andrew Sholl said: ‘Sue will be taking some time off and will be assessing her options.’
Robertson has formerly worked as head of corporate affairs at Channel 4, director of corporate affairs at United Broadcasting and Entertainment and press secretary to Dr David Owen MP.
She has also worked as a BBC producer on Panorama, Question Time and Newsnight.
Robertson leaves at the same time as channel controller Richard Woolfe and director of strategy Charles Constable.
On 31 October, chief executive and chairman Dawn Airey, managing director Mark White, director of finance David Hockley, director of legal Paul Chinnery and head of HR Natasha Adams will depart.