Über, the incumbent, had picked up the account in 2013 from Enter, now known as George & Dragon.
McCann Manchester will work on strategy, creative, production and point-of-sale activity for the brand, which spent £23.2 million on advertising in 2014.
Tim Marsden, the marketing and e-commerce director at Harveys, said: "The McCann team has an excellent retail pedigree, having worked for Aldi for more than a decade, and the team demonstrated real and original insight into our brand and the challenges we face."
McCann Manchester will begin working on the account immediately. RP2, the media incumbent, is unaffected.