The agency picked up the account after a pitch, and will oversee the restaurant chain's advertising, digital marketing and in-restaurant communications.
It is also understood that Eden, Adam & Eve's media arm, will handle Pizza Express' communications planning work.
Pizza Express has previously used Work Club to handle its advertising campaigns. It has also worked with Isobel and Archibald Ingall Stretton on marketing projects.
Adam & Eve's first campaign for Pizza Express will launch in the next few weeks and follows the biggest brand refresh in its 46-year history.
Revealed earlier this week, the rebrand includes a new black-and-white logo, as well as fresh restaurant designs and a revamped menu. Pizza Express has also announced plans to open a further 200 restaurants in the UK.