Born in London, Watson was a "professional student" until 1990, when she enrolled as an acting student at the London Drama Studio. She began appearing in theatrical productions and by 1992 was a member of the Royal Shakespeare Company, where she met her husband, actor Jack Walters and appeared in such productions as "The Taming of the Shrew" (1992) and "The Children's Hour" (1994).

Watson reportedly was cast as Bess in "Breaking the Waves" after it was turned down by the nudity-shy Helena Bonham Carter. She was mesmerizing as a deeply spiritual woman who was willing to do anything to spare her husband from pain. Watson earned raves, was named Best Actress by both the New York Film Critics Circle and the National Society of Film Critics and garnered a Best Actress Academy Award nomination for her debut. She segued to a period piece as another headstrong young woman in the 1997 British TV production of "The Mill on the Floss" before starring with Christian Bale in "Metroland" (also 1997), a comedy drama about an unconventional couple in 70s London. (The film received limited release in Europe and was released theatrically in the USA in 1999.) Watson was then tapped to play the Irish lass whose former lover (Daniel Day-Lewis) returns to complicate her life in "The Boxer" (1997). In 1998, she offered a showy tour de force as the eccentric cellist Jacqueline du Pre in the biopic "Hilary and Jackie" (earning a second Oscar nomination as Best Actress) before undertaking another role as an Irishwoman, this time the put-upon mother of a large brood in the film adaptation of Frank McCourt's award-winning memoir "Angela's Ashes" (1999). In 2000, Watson appeared in a little-seen and less-praised comedy called "Trixie." In 2001, she had a featured role in the award-winning Robert Altman comedy "Gosford Park." In 2002, Watson sampled both ends of the spectrum, playing in the well-received romantic comedy "Punch-Drunk Love" from director Paul Thomas Anderson and in the crime thriller "Red Dragon," in which she was very effective as the unsuspecting blind girlfriend of the serial killer the Tooth Fairy (Ralph Fiennes). Her next 2002 releases was "Equilibrium," a sci-fi parable she shot two years earlier. On stage Watson was nominated for 2003 Laurence Olivier Theatre Award for Best Actress of 2002 for her performance in "Uncle Vanya" performed at the Donmar Warehouse. On the small screen, the actress appeared in the HBO biopic "The Life and Death of Peter Sellers" (2004), playing the first wife of the brilliant but troubled screen comedian (Geoffery Rush).