The agency is understood to be in final negotiations with McDonald's for a major new health drive.
The campaign brief is believed to encompass three elements: communicating McDonald's healthy credentials, the nutritional value of its food and the ethical stance it takes on sourcing ingredients.
Last year, the company used a mass direct mail campaign to convey these brand values, but this will be the first time it has applied the strategy above the line.
TBWA pitched against the UK incumbent, Leo Burnett, and DDB Worldwide. The TBWA and DDB networks both handle McDonald's in other markets.
The news is not believed to affect Leo Burnett's hold on the main UK ad account, but TBWA's appointment will come as a blow to the network, which also saw DDB London walk off with a portion of McDonald's business last year. DDB was briefed to produce a campaign promoting McDonald's salads.
The pitch was handled by Dominic Rowell, McDonald's head of marketing. Its vice-president and marketing chief officer, Laurie Morgan, is on maternity leave.
Earlier this month, the company announced it was closing 25 of its outlets after falling sales. One of the issues it faces is increasing pressure for people to eat more healthily.
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