The agency will now handle all on- and offline media for the company, apart from the search marketing account, which has been handed to the search specialist Greenlight.
The move brings to an end Vodafone's 12-year relationship with OMD. The other competing agencies - MPG, Universal McCann and Walker Media - were knocked out at the chemistry stage.
The win adds to Carat's triumphs at the end of last year. These included Kellogg, which it won from Mindshare, and the consolidation of the Santander account.
Carat lost out to OMD in a pitch for the consolidated £650 million Renault/Nissan media account across EMEA at the end of last year.