Rise will merge with digital strategy agency Contented to create Eden State. Contented launched last month; its clients include Cutty Sark Whisky and R&R Ice Cream.
Simon Mathews, who co-founded Rise, will become chief executive of Eden State, with responsibility for leading the company's expansion strategy through further acquisitions and the development of more digital, creative and media agencies.
Rise, which was co-founded by Ollie Joyce in 2003, counts the COI, Network Rail and Channel 4 among its biggest clients. The agency is Eden State's first acquisition.
Mathews was previously chief executive of Equinox Communications and managing director of Publicis Groupe's Optimedia. He has also held roles at Saatchi & Saatchi and Young & Rubicam.