The four-year business was won from PHD, which had been handling the account on an interim basis since September last year. As well as PHD, MediaCom also saw off competition from MindShare and ZenithOptimedia.
The pitch was overseen by Digital UK director of communications Beth Thoren and chief executive Ford Ennals. Thoren said MediaCom had a strategic edge on its rivals.
"It was a very competitive pitch and a difficult decision but MediaCom had an edge in strategic thinking which, coupled with their passion for TV, will help us increase awareness and understanding of digital switchover as we ramp up our activity," he said.
Nick Lawson, chief executive of MediaCom, said: "We are very proud to be working on the most important TV project of our generation."
The first Digital UK public communications campaign, created by Abbott Mead Vickers BBDO, will run on the BBC and commercial TV later this year. Digital UK will also launch regional campaigns in the West Country, Wales and Granada ITV regions.
Seperately, the group is seeking an online agency to handle over £1m of marketing activity and Proximity London, OgilvyOne, Partners Andrews Aldridge and Rapier are currently pitching for the DM business.
Digital UK, formerly SwitchCo, is the government-appointed organisation co-ordinating the switchover from analogue to digital TV.
The switchover process will be conducted via ITV regions, with the Border region first in 2008 and Ulster last in 2012.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the Forum.