Optimedia, which handles a number of clients in the fashion sector, will work on the Gap business in the key British, German and French markets.
The pitches were held at Gap's San Francisco headquarters at the end of last month.
At one stage, the pitching agencies feared the pitch would be cancelled as the client considered taking its media in-house.
The loss of the Gap account comes at the end of a miserable year for Mediaedge:cia, which has been hit by a series of client reviews since the agency was formed at the beginning of the year.
It has suffered the losses of both Wrigley and Daewoo and is currently defending Singapore Airlines and the Wyeth pharmaceutical accounts from rival networks. The agency is now undergoing a management restructure.
Gap's recent history has also been challenging. It has been put under increasing pressure from more recent rival entrants into the high-street fashion sector such as Zara and Uniqlo and suffered a 37 per cent drop in its second-quarter profits.
In a bid to improve its fortunes, Gap recently enlisted the Hollywood film directors Cameron Crowe, Roman Coppola and the Coen Brothers for its advertising campaigns.
No-one at Optimedia would comment as Campaign went to press.