The agency won a three-way pitch to promote the Whitbread-owned brand.
Its campaign will target the national, women's and men's consumer media, stressing the Costa drinks' taste.
Costa was formerly promoted by CompanyCare.
Separately, Whitbread has ended the review of its restaurant brands' PR that it began earlier this year (PRWeek, 29 April), opting to stick with its incumbent agencies.
Euro RSCG Biss Lancaster will continue to promote Brewers Fayre, while CompanyCare will remain on the Beefeater and TGI Friday's accounts.