During its time on the account, the agency has created a number of campaigns.
They include the "Gold Spot" cinema ad last year that showed a series of holiday photographs projecting how the restaurant had brought families together over the last decades. The strapline was: "Family fun since 1958".
W&K won the Pizza Hut business from Abbott Mead Vickers BBDO in February 2005 after a three-way pitch against Clemmow Hornby Inge, WCRS and Bartle Bogle Hegarty.
Neil Christie, the managing director of W&K, said: "We've had a great relationship with Pizza Hut over the last three years but we feel that moving forward we're not the right agency partner for them.
"We've discussed this with Pizza Hut and decided to part amicably to allow them to move on with the next phase of development of their business."
Hugh Wood, the marketing director of Pizza Hut UK, said: "We've enjoyed working with W&K over the past three years and we'll continue to do so over the next few months as we conduct a pitch process.
"After three years both parties feel it's time for a change and we part on good terms and wish them the very best for the future."
"We are focused on a major brand relaunch at the end of 2008 and are very excited about working with a new agency that can deliver on a campaign of that importance".