The appointment of James is part of a wider restructure of the group that sees Alastair Bannerman, the current managing director of Starcom UK, move to the role of chief client officer across the group.
Both Bannerman and James will report to the group chief executive, Stewart Easterbrook, and James will work alongside Steve Parker, the managing director of the sister agency MediaVest UK.
James left OMD, which he joined in 2004, last year to become the UK sales director of Yahoo! but eventually decided not to take the role.
He was previously the managing director of Manning Gottlieb OMD and, briefly, of MEC before leaving to run Naked Ambition, the joint venture between Naked Communications and Grey.
Bannerman's move to a wider group role follows the recent promotion of John Antoniades, the client managing director EMEA, to the new London-based role of multinational client operations director EMEA. Antoniades also reports to Easterbrook.
Easterbrook said: "At the start of the year, we outlined an ambition to create local offices capable of genuinely global reach. To achieve this, we need a strong, focused leadership team that best utilises the talent we have as a group."