MPG won the business after a pitch, run by the AAR, against the WPP-owned MediaCom North and Feather Brooksbank. WPP's Mindshare, the incumbent, did not repitch for the business.
Mindshare has held the Admiral media account since July 2007, and before that it had been split between Starcom MediaVest and MediaVest Manchester.
Admiral called a review of the business, which includes media planning and buying for the insurance brands Admiral, Bell Direct, Diamond, and elephant.co.uk in March this year.
The £25 million media account for Admiral's Confused.com price comparison site was awarded to PHD in March after a separate pitch process.
Emma Dunn, the media strategy manager at Admiral, said: "MPG really impressed us throughout the pitch process. Its strategic approach and understanding of our business made the agency the obvious choice for moving our business forward."
Marc Mendoza, the MPG chief executive, said: "We are delighted to win Admiral, and we are proud that our proposition proved to be a success in such a competitive pitch process. It's fantastic to be working with a collection of prestigious insurance brands, and I know we can work together to significantly grow these brands."
Established in 1993, Admiral operates predominately in car insurance and price comparison.