The fast food chain calls its first plant-based offering "The Imposter." The burger, who uses a Quorn fillet and vegan mayo, will be sold at selected restaurants for four weeks from June 17.
Quorn is a meat substitute that gets the protein content from a fermented fungus. KFC describes burger as "a triumph of deception".
KFC is the latest in a series of restaurant chains and food producers to try to capitalize on the public's growing appetite for meat alternatives.
Globally, the retail market for meat substitutes can grow from around $ 18.7 billion in 2018 to $ 23 billion in 2023, according to Euromonitor International.
The company expects total revenues to exceed $ 210 million this year, up over 140%.
Animal-owned groups praised KFC for offering the vegan burger.
"We are confident that it will be a great success with the skyrocketing number of vegans, vegetarians and flexitarians around the UK," said Dawn Carr, director of vegan business projects at PETA.