Purser will report to the managing director of Iris Digital UK, Tom Poynter, and focus on building the agency's digital strategy capabilities.
The move follows a restructure at Iris last year that saw Poynter made the managing director for Iris Digital in the UK. The joint managing directors, George Nimeh and John Baker, were promoted to directors of digital for Europe and the US respectively.
Purser spent four years at LBi, where he worked on planning, business consulting and research, as well as on the Unilever and BT accounts. Before that, he worked at Digitas Modem for two years and ran his own digital brand consultancy, working with companies such as Tesco, HBOS and Microsoft.
He said: "Digital is no longer solely the preserve of digital agencies, as it is now at the heart of almost every marketing programme."