The agency already holds the media account for the Gap Group, which owns Banana Republic.
The brand's first stores will open in the UK this year. Banana Republic has ambitious plans to expand overseas having already opened 13 outlets in Japan since autumn 2005. It also recently announced plans to add branches in Asia and the Middle East through franchise agreements.
Banana Republic has performed strongly in the US, where it enjoys a premium positioning and operates at a significantly higher price point than Gap.
Its first UK store, which will be located in London's Oxford Street, will open this March.