Naked is launching Naked Ambition in an attempt to manage its growth without sacrificing its small-agency culture.
John Harlow, a partner and co-founder of Naked, said: "Matt is one of the most impressive people we have met in the industry and he was the only candidate we wanted to spearhead the next Naked venture. Naked Ambition reflects our strategy of collaborating with the best people in the business, diversifying into a family of companies and is a reflection of intense client interest."
He added that James was one of a number of partners who would be hired and given equity in the venture.
However, the news was a blow to Rob Norman, the chairman of Mediaedge:cia, who only appointed James in August.
Norman said: "On reflection, I am pretty sure Matt would have taken this job before coming to Mediaedge: cia if he had been offered it before. My regrets are three-fold: I'm disappointed he didn't help me and the team achieve our ambitions; I have regrets for the staff, because when you appoint a managing director, they commit to them, and I also have regrets for the one or two clients that he has built a relationship with. This is a bump in the road - an unwelcome one - but life goes on."
Before joining Mediaedge: cia, James took a year out to set up a media strategy and content business called Maguffin. Before that, he was the managing director of Manning Gottlieb Media.