She replaces Simon Eyles who earlier this year moved to the role of head of private label marketing at Asda.
Priestley has worked for the British potato industry body for ten years, firstly as director of marketing and communications, and for the last seven years as chief executive.
She also has marketing and commercial experience in industries including hotels, broadcasting and food service distribution.
Nick Vermont, McCain Foods chief executive, says: “Coming from the Potato Council, Helen has a deep understanding of our core ingredient, the potato, and understands the value that McCain places on its relationship with Britain’s farmers.”
In May, McCain Foods revealed plans to create a TV programme, The McCain Track and Field Show, to help promote its £10m investment in athletics.
The show, commissioned by Channel 4, premiered on 26 July.
Meanwhile, Eyles joined the supermarket in April and now oversees Asda ranges including Extra Special and Smart Price.