Ono is the wife of McCartney's late Beatles collaborator John Lennon, who was shot and killed in New York City in 1980.
McCartney told Rolling Stone magazine in a 2001 interview he avoided Lennon tribute events because it was "difficult" to see Ono.
But in a new chat with the magazine to be published Friday, McCartney acknowledged, "She's badass," then chalked up their reconciliation to "time, the great healer."
"I thought: 'If John loved her, there's got to be something. He's not stupid.'"