The pitch shortlist included Publicis Groupe's Starlink, WPP Group's Mediaedge:cia, independent Palisades and the buying incumbent, Omnicom Group's PHD.
The assignment includes the main Gap range along with Gap Body, Baby Gap, Gap Maternity and Gap Kids.
The San Francisco-based firm put the account up for review in April.
Previously, most of the company's media planning has been done in-house.
The spend for the client during 2005 was approximately $100m. Gap is expected to increase this amount during 2006 to compete with rival high-street clothing retailers.
Last month, Naked won the brief for Gap's European communications strategy. It will work with Gap's main media agency, ZenithOptimedia, on "customer segmentation". Gap's global advertising is currently handled by US agency Laird & Partners.
The chain has about 3,100 stores worldwide and observers have stated that it has been hindered by its size in responding to customer trends.
Carat confirmed that it had won the planning business for the brand.
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