At M&C Saatchi, Harrison will be responsible for ramping up the agency’s international new business.
She will be based in London and will report to Moray MacLennan, the chief executive of M&C Saatchi Worldwide.
Harrison joins the agency from Formula One Management, where she was marketing and sponsorship director for nine months, charged with developing new strategic partnerships for the sport.
Prior to that, she worked at Leo Burnett’s luxury division, Atelier, as deputy managing director for a year.
Harrison has also worked at agencies such as Euro RSCG, JWT London, and Publicis.
She said: "M&C Saatchi has a great brand, a unique structure, a compelling philosophy of brutal simplicity of thought, and some great people. This unparalleled combination will give me a head start in our new business growth plans."
M&C Saatchi officially launched its New York office last week after a year of recruiting.