• Speaks German fluently.
• Daughter Of TV talk show host Wally George.
• Was engaged to Leonard Cohen.
• Second daughter, Veronica, born in Los Angeles. [31 March 2001]
• Has a half sister who was born in 1989. Rebacca has never made contact with her.
• Her last name was changed as a child, when her step-father Richard De Mornay adopted her.
• She attended the radically alternative English boarding school "Summerhill".
• She has several half-brothers and half-sisters who she has never met.
• Took her stepfather's name (De Mornay) legally at the age of 5 when he adopted her.
• Granddaughter of Eugenia Clinchard
• Gave birth to a daughter, Sophia, by Patrick O'Neal (Ryan's son). [1997]
• Sister-in-law of Tatum O'Neal

Rebecca was born in northern California, and was raised by her mother Julie and step-father Richard De Mornay until his death when she was 5 years old. Rebecca's mother then moved her and her half-brother Peter to Europe, where she was raised primarily in England and Austria. Rebecca graduated "summa cum laude" from a German-speaking high school in the Austrian alps, and still speaks fluent German and French.

She began her acting training in Los Angeles at Lee Strasberg's Institute, became an apprentice at Francis Coppola's Zoetrope Film Studio, and soon thereafter made her film debut opposite Tom Cruise in the box office hit Risky Business (1983), in which she gave a seductive and critically-acclaimed performance as a street-wise call-girl. She went on to international stardom with her portrayal of a chillingly twisted nanny in the hugely popular The Hand That Rocks the Cradle (1992). Other acclaimed film work includes Runaway Train (1985) (with Jon Voight), The Trip to Bountiful (1985) (with Geraldine Page), Backdraft (1991) (with Kurt Russell).

Network television work includes the tour-de-force role of Arlie in the stellar Getting Out (1994) (TV) (based on Marsha Norman's play), the tragic title character in Dominick Dunne's An Inconvenient Woman (1991) (TV) (with Jason Robards), the remake of "The Shining" (1997) (mini) (produced by Stephen King), a multi-episode story-arc about a cancer survivor on E.R. (1999) and Hallmark Hall of Fame's Night Ride Home (1999) (TV) (with Ellen Burstyn).

On stage, she starred as Billie Dawn in Born Yesterday (1988) at the Pasadena Playhouse, as Charlotte Corday in Marat/Sade (1990) at the Williamstown Festival, and as Anna in Closer (2000) at the Mark Taper Forum. Rebecca's directing debut was with a segment of Showtime's The Outer Limits starring John Savage and Frank Whaley. Rebecca currently resides in Los Angeles with sportscaster Patrick O'Neal, and their daughters, Sophia and Veronica.