The incumbent on the business was the7stars, which picked up the account in February.
Warren Evans' media activity is skewed towards press, but it is looking to explore advertising in new channels.
M.i. Media, which is run by the former MediaCom directors Clive Howse and Lee Boden, works in partnership with Arena Media. It now operates from the Havas-owned agency's London office and has access to Arena Media's digital resources.
David Geer, the managing director at Warren Evans, made the appointment.
Howse said: "While Warren Evans already has a very strong brand, we feel that opportunities exist for us to make a positive impact on its business."