She replaces Simon Eyles, who left the frozen-food company to become head of private-label marketing at Asda.
Priestley has worked for the British potato industry body for 10 years and previously held a marketing position at the organisation.
Last week, McCain aired its ad-funded TV programme, The McCain Track and Field Show. The Channel 4 show is part of the brand's £10m investment in athletics.
McCain has embarked on an aggressive NPD programme over the past year and extended its brand into frozen vegetables and luxury chips.