The 'London Unlimited' campaign brings together the efforts of the Mayor's Office, VisitLondon, inward investment group Think London and student body London Higher - which have hitherto handled promotional work individually.
The campaign is designed to run up to, and possibly beyond, 2012 with four agencies hired for the first 12 months of the drive.
VisitLondon's retained agency, Freud Communications, will lead the campaign.
Edelman is managing the US, with Hill & Knowlton targeting the Chinese market. Finsbury Communications, meanwhile, is handling LSE listings.
The offensive aims to position the city as a great place to work, live, study and relax. Other than encouraging inward investment, the priority is to access markets such as China, Russia and India, said VisitLondon chief executive James Bidwell.
'We want to target high-level opinion formers, the type of people who are influential on deciding where businesses locate, via titles such as Newsweek and The Wall Street Journal,' he said.
The campaign will also encourage film and TV crews to use London locations.
VisitLondon said there was a discrepancy between how London was perceived and the reality of the city, particularly among people in emerging markets.