In a statement from the broadcaster today, it was announced that Mannion, who joined ITN in 1979, will leave his current position in July to start in his newly created post as special advisor to John Hardie.
The new role will see him influence ITN's strategy and policy at a corporate level as well as advising on future planning, new business opportunities and revenue growth outside of ITN's core contracts, the release added.
"This has been a huge decision for me but, after a decade in my current role, it feels the appropriate time for me to do other things," Mannion said.
"I am privileged to have worked at ITN with some of the greatest TV news professionals of our time and I am genuinely delighted to be taking on my new role working closely with my CEO John Hardie."
Hardie added that Mannion is a "force of nature whose impact is evident in every part of ITV News".
"He leaves ITV News on a real high, with News at Ten named Programme of the Year by both the RTS and BAFTA - just the latest in a hatful of industry accolades and achievements."
Since joining ITN Mannion has been editor of ITV News, GMTV, Tonight with Trevor McDonald and the Cook Report, and the deputy editor of Channel 4 News.
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