The agency will be handling the launch of a new cook in sauce product range to drive trade and consumer awareness.
The Greencore-produced line is made under licence for Aunt Bessie's and includes six varieties.
The brief was won following a pitch in October and initially runs as a six month project which will include media relations, sampling and promotions.
Account director Olivia Holcroft will lead the account, reporting into Christine Morgan, Good Relations consumer director.
The agency already handles consumer and trade PR for Aunt Bessie's itself, an account it won in May.
Greencore Grocery is part of the wider Greencore Group, which is one of Europe's biggest manufacturers of convenience foods and ingredients.