
The Omnicom-owned agency was the incumbent on the £18.7m business for music retail chain HMV, while sister agency PHD held the £5.3m business for Waterstone's bookstores.
OMD beat PHD, Starcom and MediaCom to win the consolidated media planning and buying business in the UK.
The HMV Group owns Waterstone's and 730 stores in eight countries.
It is understood that the review, which took several months, was managed internally by HMV without the use of an intermediary auditing agency.