Nunn, currently director of digital and direct, will work alongside Robert Ffitch, who has been appointed to the OMD Group Board, and Neil Hurman.
Nick Manning, chief executive of OMD UK Group, said: “As a result of the outstanding contribution that Phil has made to the agency since joining last year, I am delighted to give him a significant role in its future direction.
“In the immediate term, the agency will be led by Robert, Neil and Phil and I will help them determine the future direction and strategy for MG OMD.
“We are extremely fortunate to have one of the best and most experienced boards in the industry, and this gives me the opportunity to spend time this autumn reviewing the ideal future shape of the management team for the next five years.”
Speaking of Ffitch’s promotion to the group board, Manning said: “I can’t speak highly enough of Robert. He has Manning Gottlieb running through his veins and has lots of good ideas about the future direction of the agency. I look forward to Robert’s contribution to the development of the Group.
He added: “Meanwhile, I’d like to thank Alison for the contribution she has made to the agency.”