Carat, led by DAN chief executive Tracy De Groose and managing director Matthew Hook, seized the initiative by employing the Government's former COI leaders Mark Cross and Jon Hopkins after the consolidation of the business four and a half years ago.
The media agency will now handle all of the Government's media buying business for the next four years.
No-one from Carat or Dentsu Aegis Network was prepared to comment on the news.
Other agencies vying for the business with M4C and Carat were Omnicom Media Group and ZenithOptimedia.
The media buying account includes all government media campaigns, both domestically for bodies such as Public Health England and the armed forces, and abroad for VisitBritain.
All those involved in the pitch are now believed to be in a 10 day "cooling off" period, where any major issues or objections can be raised before Carat is officially appointed.
Sorrell's WPP created M4C from a consortium of specialists from MediaCom, Mindshare and Mediaedge:cia when pitching for the business in 2009/2010. It is run by Peter Kemp, the managing director.
The future for M4C and its team of more than 40 media specialists was unclear at time of publishing.