Newgate secured the account, which is understood to be worth six figures, following a competitive pitch involving several agencies.
Newgate is to support 2 Sisters, which owns brands including Goodfella's and Fox's Biscuits, in all its food safety and animal welfare campaigns, and its "ongoing expansion and modernisation programme".
The role will include media relations, stakeholder and political outreach and support in financial comms.
At a trading update last month, 2 Sisters said it planned to make a "targeted investment" in its facilities. The company reported like-for-like growth of 1.1 per cent in its third quarter, and said its chilled division had almost recovered to pre-horsemeat scandal levels.
Newgate's appointment also follows recent campaigns by 2 Sisters to reduce the prevalence of campylobacter in chicken. The food manufacturer announced it would remove all antibiotics defined as critically important to human health from its poultry production.
Nick Murray, director of communications for 2 Sisters, said: "We were impressed by Newgate’s deep understanding, innovative ideas and integrated approach. This is a critical appointment in the development of communications that befit a company with the reach of 2 Sisters Food Group."
Jonathan Clare, executive chairman of Newgate, said: "We are delighted to have been appointed by 2 Sisters Food Group at this important stage in its development. The success of our approach shows the depth of the multi-disciplinary offer we have developed at Newgate."
Birmingham-based 2 Sisters, headed by Ranjit Singh Boparan, produces around a third of all the poultry consumed in the UK as well as ready meals, sandwiches, biscuits, pizzas, pies and other food products. In 2011 it bought Northern Foods and in 2013 purchased the UK arm of Dutch red meat group Vion.