The agency won the account after a head-to-head pitch with Universal McCann, which handled the £11 million RHM planning and buying business. Premier Foods bought RHM for £1.2 billion in March.
The outcome means that MediaVest has captured brands including Hovis, Sharwood's and Mr Kipling to add to the Premier brands, such as Branston, Campbell's and Fray Bentos, it already held.
Speculation has surrounded a consolidation of Premier's ad agency relationships, but a review is not expected in the short term. Premier's five agencies are: CHI & Partners, DDB London, Delaney Lund Knox Warren & Partners, McCann Erickson and Publicis.
Premier Foods has recently been aggressive in making acquisitions. Last year it bought the Campbell Soup Company ahead of the acquisition of RHM. The company hopes that the media consolidation will create savings across the combined business.
Universal has held the RHM account since 2004 and won Premier Foods after a pitch last December.