The agency won the business after a three-month pitch process, and will now be responsible for handling the marketing activity for the radio broadcaster's two flagship brands, Capital FM and the Heart Network.
Karmarama was previously the incumbent on the Global Radio business, but the agency was forced to part company with the broadcaster in March after it secured a place on the BBC's £20 million advertising roster.
Karmarama had worked on the Global Radio business for just under two years, most recently launching a TV ad for Capital FM featuring artists including Nicole Scherzinger, The Saturdays and The Black Eyed Peas.
WCRS&Co will now take responsibility for rolling out a number of integrated marketing campaigns for Capital FM and Heart. The focus is thought to be to build on the current success of the Capital brand and to revitalise the Heart offering.
In the latest Rajar listening survey, both stations performed well for quarter two, with reach for the Capital network up 2.4 per cent from the first quarter of 2011, and the Heart network up 3.4 per cent in the same period.
However, in London Bauer's Magic 105.4 performed better than both stations to become the biggest in the capital in terms of hours and reach.