Susan Gilchrist, senior partner in Brunswick's London office, is to relocate to New York in April to head the agency's operations in the country.
She will take up the newly created role of US managing partner and run its three US offices - New York, Washington and San Francisco - alongside senior partner Steve Lipin.
Gilchrist has been senior partner at the firm for four years and has become one of the key names in the retail sector, with clients such as Burberry and HMV.
Before moving into PR, she was retail correspondent for The Times.
Her London role will be taken by Brunswick partner Nick Claydon, the ex-comms head of British Airways.