The pair won the business after a pitch managed by the AAR. VCCP, Beattie McGuinness Bungay and Farm were also involved.
Krow and EGS will be tasked with developing Pets at Home's first nationwide campaign, as it looks to expand next year. The company, which was founded in 1991, has more than 190 branches and plans to open 20 more in 2008. The stores, most of which are in out-of-town retail parks, stock more than 4500 product lines from food to toys. The company also owns Companion Care, which offers a 24-hour vet call-out service.
In October, Pets at Home handed the role of marketing director to Gillian Buttree, former marketing and business development director at Experian.
Last month Pets at Home's owner, private equity group Bridgepoint, said it was preparing for a possible £600m sale or flotation of the chain.
Pets at Home was unavailable for comment.