The appointment follows a swift pitch process, which also involved the incumbent, ZenithOptimedia, MindShare, PHD and MediaCom.
Walker Media's strong retail credentials, with clients including Marks & Spencer and Dixons, helped secure its appointment. KFC was also looking for an agency with a clear understanding of its business issues.
Zenith Media had originally captured the business in 1998 and the account still remained with the agency following its merger with Optimedia last year.
KFC's marketing director, Claire Harrison-Church, made the appointment.
It comes almost a year after she appointed Bartle Bogle Hegarty to handle KFC's creative.
Phil Georgiadis, a partner at Walker Media, said: "We were able to articulate to KFC what they wanted to say themselves. What's interesting about all retail business - but specifically the ones you'd call 'entertainment retailers' - is that the media has to perform two roles. It has to drive people through the doors on a daily and weekly basis and compete against global rival companies for brand performance too."
The fast food company's spend is largely geared towards television with a small percentage on press and outdoor campaigns.
KFC is owned by theUS corporation Yum! Brands, which owns Taco Bell and Pizza Hut. PHD handles Pizza Hut's UK media planning and buying.
Bartle Bogle Hegarty landed the creative account at the end of last year.