Channel 4 Radio has been billed as a younger and livelier version to BBC Radio 4, while E4 Radio and Pure4 are spin-offs from the TV channels.
Shennan's start date is yet to be confirmed but once in the role, he will report directly to chief executive Andy Duncan and will join the channel's executive management team.
Shennan said: "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 was appointed controller of Five Live in August 2000, overseeing the launch of sister network Five Live Sports Extra. Since 2004 Shennan has also had managerial responsibility for the BBC Asian Network.
Prior to Five Live, he held a number of senior roles in BBC Sport including head of BBC Sport from 1998 to 2000.
Duncan said: "Bob has helped make Five Live one of the UK's most popular and admired networks. It's a coup to attract someone of his profile and experience - his appointment is a boost to our plans as we move from a successful bid stage towards delivery."
Shennan will work closely with Schwarz, Channel 4's current director of radio, and also with Kevin Lygo, director of television and content, on developing editorial and commissioning policy for the new stations.
Schwarz has been promoted to join the Channel 4 board as new business and corporate development director, where she will take over responsibility for Channel 4's new business and corporate development, looking for new investment and business opportunities across all platforms.
She replaces Rod Henwood who last week announced his decision to step down.
Schwarz, who oversaw the successful Channel 4-led bid for the second national commercial DAB multiplex, will chair the 4 Digital Group consortium, which will manage the new DAB multiplex. In addition she will manage relations with shareholder partners, as well as sitting on industry bodies including the Digital Radio Working Group.
Duncan said: "Nathalie's promotion is in recognition of the role she has played in developing and launching the radio business. Her in-depth knowledge of the radio sector will continue to prove valuable to us, while her new responsibilities play to her strong track record in growing businesses within the media industries."
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