McCain has appointed the agency to handle consumer, trade and corporate comms, and direct comms with restaurants and caterers. Nexus was appointed after a four-way pitch that included the incumbent.
The move comes as the frozen food company looks to reassure consumers on the healthiness of its potato products, including promoting the 'It's All Good' ad campaign aimed at emphasising the purity and nutritional value of McCain's products.
The Nexus team is being led by director Jane Baerselman, who reports to McCain marketing director Helen Priestley.
Baerselman said: 'There will be support for the It's All Good campaign. Also, we're looking at putting together programmes supporting a mixture of the individual brands, which are all putting together different briefs.'
As well as its flagship oven chips, the Scarborough-based manufacturer also sells potato wedges, frozen vegetables and frozen pizzas.
McCain Foods is the top-selling retailer in the frozen potato market, making £270m per year.
Separately, F-H is believed to be in talks with Bell Pottinger head of public health and behaviour change Claire Cater over its vacant UK MD role.
Cater has worked at Bell Pottinger for five years, before which she worked as director of corporate comms at APCO Worldwide.
She has also worked as head of public and corporate affairs at Bupa.
F-H is expected to appoint a new UK MD by the end of September.
F-H regional president Kevin Bell said no appointment had been made: 'We have talked to more than 100 talented individuals over the past couple of months and we will be making an announcement as soon as we have completed our search.'