Holyfield's attorney, Jim Lewis, confirmed last night that the World Boxing Association and International Boxing Federation champion signed a contract after a four-hour meeting with King.
Lewis, who holds the World Boxing Council title, has still not signed his contract, but Thomas said that following Holyfield's signing, King called Panos Eliades, Lewis's promoter, and was told "send us a contract and we will sign".
The fight will be on TVKO, the pay-per-view arm of Home Box Office, the American cable network which has a contract with Lewis. King indicated during his trip to Britain this week that the major obstacle to the fight, which network would screen it, would be overcome because he would defer to Lewis's demands and fight on HBO. King's fights are usually on Showtime. However, Thomas said: "Don still needs to reach final agreement with HBO."
The fight is expected to take place in Las Vegas in February or March, with Holyfield set to receive $20m (pounds 12m) and Lewis $8m.
Holyfield made an IBF mandatory title defence by outpointing Vaughn Bean on 19 September in his hometown of Atlanta. He was supposed to make a mandatory defence of his WBA crown against Henry Akinwande on 6 June in Madison Square Garden, but the fight was called off after Akinwande tested positive for hepatitis B. Thomas said Akinwande still is not available to fight.
Lewis made a mandatory defence of his WBC title, outpointing the Croat Zeljko Mavrovic on 26 September at Uncasville, Connecticut.