Maddison will be the company's most senior European client handler and will work across a number of its clients, including Tesco, P&G, Electronic Arts, The Economist, Aer Lingus, OgilvyOne and John Lewis.
He joins from Epsilon client Nectar, where he was responsible for clients including EDF Energy, the AA, American Express Credit Cards, Ford and Hertz. Nectar is part of the Loyalty Management Group.
Prior to his time at Loyalty Management, Maddison was managing director of Labdirect, a direct marketing agency owned by the RPS Group. Before Labdirect he was a consultant at Expert Information Services in Australia.
Epsilon claims to have trebled in size in the past 18 months, with its UK account management team tripling in size in just eight months as a result of an increased customer service focus.
The company said that it has hired Maddison because the email business is becoming less about the technology and more focused on the delivery of strategic advice, with clients demanding greater levels of service.
Nick Christie, UK country manager for Epsilon, said: "Jon is a polished, experienced professional who has worked both on the agency and client side. He brings extensive industry knowledge from finance to FMCG and from retail to telecoms.
"The email industry is changing and Jon will be able to offer the highest level of strategic guidance and vision to our clients."