BBC Radio 5 Live's controller, Bob Shennan, is to leave the BBC to oversee Channel 4's new digital radio stations.
Bob Shennan had been controller of BBC Radio 5 Live since 2000
He becomes Channel 4's director of radio, as the company prepares to launch three networks.
These will include a speech station aimed at young people - known as Channel 4 Radio - and a spin-off from the E4 television network.
Radio 1 controller Andy Parfitt will take Mr Shennan's responsibilities until a replacement is found.
"I believe Channel 4's entry into UK radio is the most significant and exciting development in the market for a long time and I'm looking forward to leading it," he said in a statement.
Mr Shennan, 45, has been controller of 5 Live since 2000, and during this time, the station's audience reached a record total of just under seven million listeners.
He oversaw the launch of sister network 5 Live Sports Extra, and for the past three years has also had managerial responsibility for the BBC Asian Network.
The BBC's director of audio, Jenny Abramsky, said in an e-mail to staff it was "a wonderful opportunity" for Mr Shennan.