They are being employed to hand out leaflets describing the alleged cruelty in the way the fast-food chain treats its chickens. The leaflets are being distributed outside five of the chain's London restaurants on Wednesdays to Sundays between 11am and 2pm.
"We're always looking for interesting ways to get our message across," said a Peta spokesman. "Homeless people have the time and flexibility to do this and are concerned citizens too."
A spokesman for homeless charity Thames Reach Bondway said: "Homeless people are able to make their own decisions on issues of this kind. As long as they're being paid the minimum wage, we wish them the best of luck."
Peta claims that 850 million chickens a year suffer crippling injuries.
"If KFC executives treated cats or dogs the way they treat chickens, they could go to prison," said Sean Gifford, director of European campaigns at Peta.
A KFC spokesman said: "KFC is committed to poultry welfare. We select suppliers that meet or exceed British and EU regulations on quality and welfare, and audit their performance."
Peta plans to continue the campaign indefinitely.