The agency takes up the account this week after winning a competitive pitch.
It has a wide-ranging brief that includes trade, consumer and thought leadership work.
John Mulvey, marketing manager at Cawston Press, whose drinks are sold by a number of retailers nationally and more recently in Benelux and North America, said: "Seven Hills is well known for its campaigning work – the work it did with Ella's Kitchen in particular was very impressive, the way it has built that brand on a campaigning platform – and we felt there were some similarities between us and that business."
According to its website, Cawston's mission is "to make beautiful soft drinks, using only the best tasting ingredients and absolutely nothing artificial".
Emma Johnson, managing director at Seven Hills, said Cawston Press was "a brilliantly innovative business with an ambitious growth plan for the next three years", and that the agency would be helping it expand into new export markets.
The firm had previously spent three years working with Kent agency Piracy Corporation, which was among the firms pitching for the account in November.
Piracy managing director Martin Ballantine said: "We're sad to see it go as it’s a lovely brand, but three years is a pretty good stint. We’ve helped make it famous in the food and drink pages - as well as raised its profile significantly in the business and trade PR media."