The station will not be rebranded with the Channel 4 name and will not carry additional content from its shows such as 'Popworld' or 'Big Brother', the broadcaster has confirmed.
Oneword is a talk radio station currently operating on the national radio multiplex, Digital One, as well as Sky, Freeview and cable.
It was voted the Sony digital radio station of the year in 2003 and has almost doubled its listeners over the past year to reach more than 112,000 people.
UBC, the UK's largest radio production company, took full control of Oneword last year, paying USI Holdings £755,000 in shares for its 50% stake.
Channel 4 is believed to be paying a substantial premium to the price paid to USI Holdings.
Michael Hodgson, head of corporate development at Channel 4, said: "As we move towards a fully digital and converged world, we are actively exploring opportunities that exist across all digital platforms and UBC Media will be a valuable partner to help us further explore the radio sector."
Last September, UBC and Channel 4's commercial arm 4Ventures bought a stake in Simon Fuller's music TV show format 'Popworld' with plans to extend the brand into digital radio and sell syndicated programming to commercial radio stations.
'Popworld', which airs nightly on MTV and on Channel 4's T4 Sunday morning slot, attracts the key Channel 4 demographic of 18- to 34-year-olds and has a spin-off annual concert called Popbeach.
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