The agency secured the account without a pitch, and will now promote the station online through social media and other digital work.
Its first campaign will be launched to coincide with the upcoming Capital FM 2010 Summertime Ball, a music event hosted by the station at Wembley Stadium that will include performances by artists including Cheryl Cole, Rihanna and Dizzee Rascal.
The campaign will include the creation of what the agency hopes will be the biggestever Facebook photo wall, which will encourage those attending the event to upload their pictures.
Global Radio, which owns Capital FM, already works with a number of agencies on its advertising roster.
In September last year, it appointed Karmarama to handle advertising for Capital FM and the Heart network.