M&C Saatchi, the incumbent, was involved in the pitch. The agency picked up the business in June last year.
Fold7 has been tasked with handling all marketing for Doddle, including above-the-line, in-store, digital and experiential activity.
Paddy Earnshaw, the chief marketing officer at Doddle, said: "Our business is moving so quickly that we need a team that is capable of grasping the challenges and delivering results quickly and brilliantly."
Doddle is a joint venture between Network Rail and Lloyd Dorfman, the founder of Travelex. It has set up 35 stores in railway stations and other hubs and has taken on 70,000 members in a year.