Beckinsale is the daughter of Judy Loe (a stage actress) and the late Richard Beckinsale, a well-known television actor who died in 1979, at the age of 31. Kate's paternal great-grandfather was Burmese.

Beckinsale won first prizes in several young writing competitions. After finishing school in London, she followed in the footsteps of her parents and began her acting career. Her first role was in One Against the Wind, a television film about World War II that was first aired in 1991. Beckinsale then began studying German, French and Russian at New College, Oxford University, though she did not complete her studies (although she speaks these languages fluently). She felt that a general university background would be better for her than attending a school of performing arts.