The partnership has been in place since 2009, during which time the brand has grown substantially thanks to marketing efforts including a Waze partnership and its Coronation Street product placement deal.
Eric Tavoukdjian, commercial marketing director at Costa Coffee UK and Ireland, said the agency had been "instrumental" in delivering a media strategy to engage current and new customers.
"During the pitch process, their commitment to taking our media plans to the next level was evident and so we’re delighted to continue our relationship with them as we move our brand ahead in this competitive market," Tavoukdjian added.
Mark Howley, chief executive officer Zenith UK, said: "We are thrilled to have been reappointed as Costa Coffee’s preferred media buying agency. We see exciting opportunities to develop with the brand and we will double-down in our efforts to help the Costa team build an even more successful future."