Mediassociates will service the account in partnership with NJM's advertising and communications shop, Philadelphia-based Brownstein Group, to form a unified account.
The assignment comes as NJM accelerates its expansion beyond its home state of New Jersey.
Mediassociates will plan and buy media on behalf of NJM in New Jersey, Pennsylvania, Connecticut, Maryland, and Ohio.
Billings were not disclosed, but the announcement cited Mediassociates' proprietary Precision Branding methodology as part of the reasons for the win.
The incumbent also was not disclosed but a recent NJM campaign release credited Philadelphia-based Harmelin Media for media planning and buying on the account.