Gallop moved to New York to found BBH there in 1998 and, until September last year, was president of BBH US, before being given the role of chairman and chief marketing officer. Gwyn Jones, chief executive of BBH London, moved to the chief executive role of the New York office at the same time.
According to reports, Gallop, who considers herself "spiritually a New Yorker", plans to remain stateside. She has been with BBH for 16 years, and before setting up the New York office she helped found BBH's Singapore outpost.
In the six years since BBH New York was founded, it has built up its staff to 120 with billings of $350m and clients including Levi's and Johnnie Walker.
"When I turned 45 back in February, I started to take stock of my career. That triggered a feeling that after 16 years with a wonderful agency, it is time to move on," Gallop said.
BBH is 49% owned by French advertising business Publicis Groupe.
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