The bid, backed by a total budget in excess of £20 million, is run by the newly formed body London 2012, which saw presentations from four agency groupings.
M&C Saatchi and TIP, which owns the planning agency Unity, fought off competition from Delaney Lund Knox Warren & Partners with Naked Communications, Leo Burnett with Manning Gottlieb OMD, and WCRS with PHD. Mother is also thought to have pitched. The pitch was run by COI Communications.
The task for M&C Saatchi and TIP is to develop a communications idea that will work across media and audiences to galvanise support for the bid ahead of the International Olympic Committee's decision in July 2005.
Media buying will be by the COI roster agencies Starcom MediaVest, MediaCom and OMD UK.
London 2012, a consortium which includes the Department of Culture, Media and Sport, the Greater London Authority and the British Olympic Association, wants the agencies to take the message of London's bid to the public, politicians, the business community and the media to build momentum.
The first work from M&C Saatchi is expected to appear early next year.
It will aim to create a clear idea of what the bid stands for across a variety of media, from paid-for spots to ambient activity.
Recent surveys suggest that two-thirds of the British public back the London bid. Tim Duffy, the managing director of M&C Saatchi, said: "Support for the bid is high but the job is not to gain support but turn it into active support and advocacy - whether this is among the public, children in schools or businesses."
"Convincing the members of the International Olympic Committee and winning the hearts and minds of people throughout the UK will be a campaign like no other," Duffy added.
David Magliano, London 2012's director of marketing, said: "We were spoiled for choice. We saw five outstanding presentations but, when the dust settled, M&C Saatchi and The Ingram Partnership shone through with the greatest passion and the clearest ability to meet the brief. With their help, we're going to put together a cracking bid."
Barbara Cassani, London 2012's chairman, and Keith Mills, its chief executive, are working to bring in corporate sponsorship for the bid. Adam Crozier, the chief executive of the Royal Mail, has donated £1 million in support of the bid.