Omnicom has cut a mobile ad buying deal with Twitter worth nearly $250M during the next two years.

The ad/PR conglom gains inventory and locked-in rates at the mico-blogging site.

In announcing the deal, OMC stressed the “opportunity to deliver first-to-market benefits that impact all aspects of all Omnicom clients’ digital investments, from content to placement to measurement.”

Twitter says the arrangement is the first that it made on the ad exchange side with an agency holding company.

It bought the MoPub ad exchange for almost $250M last September.

Publicis, former merger partner with OMC, last week unveiled a $500M multi-year deal with Facebook.