O'Mara made her stage debut in a production of The Merchant of Venice in 1963, although her first film role was some years earlier (under the name Merrie Carroll) in Home and Away (1956) with Jack Warner, as her father, and Kathleen Harrison. After boarding school she attended art school before becoming a full-time actress. Her younger sister is actress Belinda Carroll. Carroll, an RAF flying instructor, and actress Hazel Bainbridge (born Edith Marion Bainbridge 25 January 1910 – 7 January 1998).

On American television, she played Caress Morell, the scheming sister of Alexis Colby in the primetime soap opera Dynasty (1986).

She also appeared as Jackie Stone in two episodes of the sitcom Absolutely Fabulous (1995–2003) and as Virginia O'Kane in four episodes of the prison drama Bad Girls (2001). On BBC television, she had regular roles in The Brothers (1975–1976), Triangle (1981–1982) and Howards' Way (1989–1990), and portrayed Doctor Who villain the Rani three times (1985–1993). In the cinema, O'Mara acted in two 1970 Hammer Horror films: The Vampire Lovers and The Horror of Frankenstein. Her other stage roles included Elvira in Blithe Spirit (1974), Lady Macbeth in Macbeth (1982), Cleopatra in Antony & Cleopatra (1982), Goneril in King Lear (1987) and Marlene Dietrich in Lunch with Marlene (2008). O'Mara made her stage debut in a 1963 production of The Merchant of Venice. Kate O'Mara (born Francesca Meredith Carroll 10 August 1939 – 30 March 2014) was an English film, stage and television actress, and writer.

Mistress of Light by K.T. Kaye