Lesley Mair, the chairman of WWAV Rapp Collins Group, is leaving to take over as the president and chief executive of Rapp Collins New York.
Mair, who has also been the managing director of WWAV's London agency for the past four years, takes up the position in April.
WWAV is looking for a successor but in the interim Chris Gordon, its group chief executive, will run the London agency. Mike Larmer, WWAV's head of client services, will take on the additional role of deputy managing director.
Mair joined WWAV in 1985 as an account director following spells on the client side at Book Club Associates, Avon Cosmetics and Diners Club International.
She was appointed to the board in 1988. In 1997 she succeeded John Watson as managing director and then replaced him as group chairman last year.
Mair's challenge is to grow the US operations of Rapp Collins. Its New York office employs 320 staff and has clients including Mercedes-Benz and Pfizer. Part of her brief is to bring about a closer working relationship between Rapp Collins agencies.
Mair said: 'There are few jobs I would ever consider leaving WWAV for but being given the opportunity to take Rapp Collins New York on to the next stage of its development is simply a challenge I could not resist.
'WWAV has strength in depth and is bigger than one person. Chris Gordon and I have worked closely together and I've worked with Mike Larmer for 12 years. The agency couldn't be in safer hands.'