Ashley Highfield controls a budget of more than £74m a year
The BBC's head of future media and technology Ashley Highfield is leaving to launch an on-demand video service for the BBC, ITV and Channel 4.
Known as Project Kangaroo, the joint venture has been described as "Freeview for the internet" and plans to offer more than 10,000 hours of programmes.
Highfield is responsible for the BBC's websites and interactive TV as well as new services such as online video.
He recently masterminded the launch of the iPlayer TV download service.
His leaving date will be announced "in due course", the BBC said.
Director general Mark Thompson said Highfield had been "pivotal in transforming the BBC for the digital age".
In 2003, Highfield was awarded the Digital Innovator internet award by The Sunday Times, who dubbed his vision of a 100% digital Britain a "tour de force".
A year later, he was named "most influential individual in technology" by online technology news site Silicon.com.
His departure creates a vacancy in one of the UK's highest profile technology jobs.
The holder of the post also oversees the BBC's research and development teams and a project to digitise the BBC's vast radio and television archives.