The media group landed the HP business, which has an estimated $1 billion in billings, after a final pitch against Mediaedge:cia.
Carat, Universal McCann and the incumbent, ZenithOptimedia, also pitched for the account, which had £3 million in UK billings during 2008 according to Nielsen.
OMG's networks OMD and PHD collaborated on the pitch and are working on possible ways of servicing the business.
In Europe, this could mean the creation of a standalone team to handle the account owing to conflict with PHD's Canon business and OMD accounts including Sony and Vodafone.
HP also appointed Omnicom agencies to handle the integrated account for its technology group. Rapp is likely to lead this activity.