Lucas told Bloomberg Businessweek that all three were signed for the new "Episode VII" film in advance of Lucasfilm's $4 billion purchase by Disney.
"We had already signed Mark and Carrie and Harrison — or were pretty much in the final stages of negotiation," Lucas said.
He added: "Maybe I'm not supposed to say that. I think they want to announce that with some big whoop-de-do."
In an interview posted Wednesday with Florida's Palm Beach Illustrated, Fisher said that she'll be coming back as Princess Leia.
Disney's Lucasfilm was coy in response. In a statement, a spokesperson for the company said, "George couldn't say whether they were signed or not and neither can we. As Yoda said, 'Always in motion is the future.' Stay tuned."
The Walt Disney Co. is producing a new "Star Wars" trilogy to take place after Lucas' original three space epics. J.J. Abrams is directing the first film. The 70-year-old Ford, the 61-year-old Hamill and the 56-year-old Fisher are expected to play smaller, supporting roles.
A representative for Ford declined to comment. Hamill's representatives didn't immediately return requests for comment.