He joins a six-strong team, whose campaign successes include Jamie's School Dinners, Lost and Desperate Housewives.
Rufus Radcliffe said: "The Channel 4 role will be an incredibly exciting new challenge that I can't wait to get started on."
Radclife joined Channel 4 in August 2000 to work on the launch of digital E4, and helped establish the digital channel's brand. He is currently responsible for E4's marketing.
For the last year he has also been overseeing the launch campaign of new digital channel More4, which launches on 10 October.
Following Radcliffe's appointment, director of marketing Cochrane will be looking to fill the newly created role of head of marketing digital channels with responsibility for E4, FilmFour, More4, their multiplexed services and any new digital channels.
Radcliffe will keep responsibility for the marketing of E4 and More4 until a replacement is appointed.
Cochrane said: "Rufus will bring additional strategic and commercial skills together with brand building experience in a multi-channel universe, all of which will serve Channel 4 well as we gear up for switchover.