The former Fallon president of international, and founding partner of the London office, was widely expected to step down after moving to Lisbon with his family last year. He will now take a sabbatical before considering his options in the autumn.
Wall, 39, joined Fallon as a founding partner alongside Robert Senior, Laurence Green, Andy McLeod and Richard Flintham in 1998.
In 2004, he was promoted to president of international, a position he took in addition to his London responsibilities. He is widely credited with being instrumental in winning the pitch for Orange, an account shared by Fallon in London and Publicis in Paris.
Wall said: "This was always the moment when I wanted to make a change of lifestyle. I remain proud and grateful for the opportunity to have worked with Pat Fallon and my partners."
Senior added: "It's classic Michael: plans the impossible and executes it brilliantly."