Ads breaking at the end of this week in national press, upmarket magazines and on the Underground are the first to be produced by Barrett Cernis since the agency won the account in early October.
Their appearance follows a torrid period for the store, which is looking to improve its fortunes after suffering a drop in tourist customers and corporate clients.
Fortnum & Mason, which recently began opening on Sundays for the first time in its 295-year history, denies that the campaign is linked to recent events. It says it wants to extend its appeal to shoppers living and working in London who have never considered visiting the store. It is also looking to tap into consumers' demands for unusual foods, which have been fuelled by foreign travel and celebrity chefs.
The ads focus mainly on the store's main offering of high-quality foods, but also feature its less well-known items, such as rare historic toys.
The ads were written by Jonathan Eley, art directed by the agency's creative director, Ray Barrett, and photographed by Karin Berndl.
The store, in which the family of the late Garfield West-on, the founder of Associated British Foods, has a majority stake, ended its stock market listing at the beginning of the year after its share price fell from a high of 900p in 1997 to below 400p.
But Justin Cernis, the Barrett Cernis managing director, said: "Our brief hasn't been to fix a troubled product but to tell people about what the store is up to. The advertising is all about getting new customers to come in."