Spark Foundry, part of Publicis Groupe, had handled the U.S. media account since January 2017.
"KFC U.S. made the strategic decision to move its media planning and buying business to Wieden+Kennedy, combining creative, media, digital, data and analytics under one integrated agency," KFC U.S. Chief Marketing Officer Andrea Zahumensky said in a statement. KFC hired Zahumensky from Procter & Gamble in December.
"In addition to its current advertising and creative scope of work for KFC U.S., the scope of Wieden+Kennedy's new assignment will include media planning and buying across all channels, including digital and social media. Spark Foundry is a talented agency, and we appreciate their partnership and work on the brand over the past year."
KFC U.S. declined to comment on whether there was a review, saying only that the change was a "strategic business decision."
Spark Foundry declined to comment.
Wieden & Kennedy's creative work for KFC, led by a series of celebrities starring as founder Colonel Sanders, helped the nation's No. 2 chicken chain achieve 13 consecutive quarters of U.S. same-store sales growth. After that strong run, same-store sales, which measure results at longstanding locations, dipped 1 percent in the fourth quarter of last year and were flat in the first quarter of 2018.
W&K was named Ad Age's Agency of the Year for 2018. The independently owned agency has handled integrated work including media for other clients including Old Spice, TurboTax and Nike.
KFC spent $231.2 million in measured media in the U.S. in 2017, according to Kantar Media.