Ullmann's father was a Norwegian engineer whose work demanded extensive travel. As a result, Liv was born in Japan and reared and educated in Norway, Canada, and the United States. During her teenage years, she studied acting in London and Norway and performed in several plays for Oslo's National Theatre. She appeared in small roles in four minor films before meeting Ingmar Bergman (Bergman, Ingmar) in 1966. When Bergman cast Ullmann in the principal role of his complex psychological drama Persona (1966), they began a long-standing professional and personal relationship. Ullmann's work with Bergman received widespread acclaim and made the actress an international star. Their collaborations—nearly all of which are regarded as masterpieces by film scholars—include Hour of the Wolf (1968), Shame (1968), Cries and Whispers (1972), Scenes from a Marriage (1973), and Autumn Sonata (1978).

Throughout her career, Ullmann worked on stage as well as on screen. She demonstrated great versatility in works by Shakespeare, Ibsen, Chekhov, Shaw, Brecht, O'Neill, and Kaufman and Hart. Her best-known stage role is that of Nora in Henrik Ibsen (Ibsen, Henrik)'s A Doll's House. It is also the only part she ever repeated, performing the role on radio as well as on stage in both Oslo and New York City. She also worked often with the famed theatrical director José Quintero (Quintero, José): as Josie in A Moon for the Misbegotten (1976), in the title role of Anna Christie (1977), in the Chekhov comedy The Bear (1978), and in The Human Voice (1979), in which she turned in a riveting 45-minute soliloquy.

Although her films of the 1980s and '90s received little American distribution, Ullmann remained among the world's most respected actresses. She tried her hand as a director in the '90s with the films Sofie (1992), Kristin Lavransdatter (1995), and Trolösa (1999; “Faithless”), for which Bergman wrote the screenplay.