The review includes the media business for Dalepak Foods, Fox's Biscuits, Fox's Confectionery and Green Isle Foods.
A number of undisclosed agencies are believed to have been invited to pitch for the business, including the incumbent.
Equinox has held the planning and buying account for Northern Foods' Goodfella's Pizza and Fox's Biscuits since 1998, and added Grassington's meat-free range, Pork Farms (now sold), Holland's Pies, San Marco Pizzas and Donegal Catch in the last media review in November 2006.
Northern Foods currently employs more than 10,000 people across the UK and Ireland and spent more than £3m on media in the 12 months to 30 April, according to The Nielsen Company, including £1.7m on TV ads.
The company reported a near 5% lift in sales for the year ending 28 March, generating £975.2m revenues and £52.7m profit. However, profits were affected by mounting pension costs.
The media review comes ahead of anticipated new marketing activity for many of its brands as the company looks to weather the current economic climate by promoting discount ranges and new commitments to ethical business initiatives, including its switch to using only free range eggs.
Northern Foods was unavailable for comment.