Ian Katz has been in his role since 2013
The editor of the BBC's flagship news and current affairs programme has left the show for rival Channel 4.
Channel 4 says Ian Katz is to become its Director of Programmes.
Katz, who is currently editor of BBC's Newsnight, was previously deputy editor of The Guardian.
Alex Mahon, Channel 4's CEO, said: "Ian is an inspirational leader who assiduously builds and nurtures talented and empowered teams.
"He has fantastic instincts and intelligence, huge editorial strength and is a proven creative and digital innovator, who lives and breathes the Channel 4 values."
In a statement James Harding, the director of BBC News and Current Affairs, said: "He took on Newsnight when there were questions about its future and, over the past four years, he has restored its reputation for fearless journalism, for powerful film-making and for rigorous intelligence on television".
"Newsnight, its viewers and the BBC will miss him".
On his move, Ian Katz said: "I'm impossibly excited to be joining a broadcaster whose unique combination of innovation, risk-taking and elan I have admired for decades as a viewer - and more recently as a frequently envious rival."
He will join Channel 4 from January 2018, having been editor of Newsnight since 2013.