She has been a major factor in the agency's revival over the past three years.
Nigel Marsh, the chief executive of the agency's Y&R Brands parent, said that, although he was disappointed with her decision, he appreciated her desire for a change. "I did everything I could to persuade her to stay and, while I'm truly sorry that she will be going, I'm delighted she is leaving an agency in such great shape," he added.
A worldwide search has begun for her replacement. Paul Fishlock, the agency's executive creative director and chairman, said several top-calibre candidates had been identified.