The agency won the account following a four-way pitch, handled directly by Nestle.
Iris is expected to work across Kit Kat’s digital retail, on-pack, social media and promotional work.
The Big Kick was behind a crowd sourcing initiative last year to choose the next permanent flavour of its Kit Kat Chunky range as it looked to increase brand awareness amongst young men.
The agency also launched the ‘Cross Your Fingers’ campaign, which used image-recognition technology to offer consumers the chance to win a cash prize of nearly £2,000.
Kit Kat also works with JWT London on its advertising and digital account, while Mindshare handles the brand’s media account. They will be unaffected by the review.