Mackenzie Phillips made the revelation in her autobiography, alleging that she slept with her father the night before her wedding.
The 49-year-old actress, a recovering drug addict, said the relationship began on the eve of her marriage to Jeff Sessler, a member of the Rolling Stones entourage, in 1979. She was 19 at the time.
In her book, High On Arrival, she wrote: “On the eve of my wedding, my father showed up, determined to stop. I had tons of pills, and Dad had tons of everything too. Eventually I passed out on Dad’s bed.
“My father was not a man with boundaries. He was full of love, and he was sick with drugs. I woke up that night from a blackout to find myself having sex with my own father.
“Had this happened before? I didn’t know. All I can say is it was the first time I was aware of it.”
Phillips, who became a household name as a child actress in the US sitcom One Day At A Time, said the relationship became consensual and she kept it secret for 30 years. She asked for understanding, saying: “Don’t hate my father.” He died of heart failure in 2001 after a long history of drink and drug abuse.
During an appearance on Wednesday’s Oprah Winfrey show to promote her memoir, Phillips said her father helped her to take drugs. The actress has had a well-documented battle with addiction and was arrested at Los Angeles airport last year for possession of heroin and cocaine.
“My father shot me up. He would put the needle in my arm and he would push the plunger in and he missed… the vein and my whole arm went numb,” Phillips recalled. “He seemed a little nervous, but at the same time it seemed very commonplace.”
Phillips is the product of the musician’s marriage to his first wife, Susan Adams.
John Phillips was the main songwriter for The Mamas and The Papas, the vocal harmony group which he formed with his wife, Michelle, Denny Doherty and Cass Elliot. They had their first hit in 1965 with California Dreamin’ and went on to sell 40 million albums worldwide, spawning such memorable songs as Monday, Monday and Dedicated To The One I Love.
He was also a founder of the Monterey Pop Festival, one of the key events of the 1967 “Summer of Love”.
The band was torn apart when Michelle Phillips and Doherty began an affair, which resulted in her being temporarily evicted from the line-up.
The group split in 1968 and John Phillips went solo. He formed The New Mamas and The Papas in the 1980s, performing with his daughter.
Michelle Phillips is the only surviving member of the band, who were inducted into the Rock and Roll Hall of Fame in 1998. Elliot, otherwise known as Mama Cass, died in 1974 and Doherty in 2007.