Naomi Ellen Watts was born on 28 September 1968, in Tonbridge, Kent, the United Kingdom, to Myfanwy Edwards, an antique dealer and costume and set designer and Peter Watts, a road manager and sound engineer for the British rock band Pink Floyd. Her parents split when Watts was only four and later, her father was found dead in his flat in Notting Hill, of an apparent heroin overdose when she was seven. Following his death, Myfanwy Edwards relocated to different places in Welsh, trying to raise Naomi and her older brother, Ben, through acting and design jobs, when Naomi attended Ysgol Gyfun Llangefni, a bilingual community comprehensive school, where Welsh was used as the primary language of teaching. After her mother remarried in 1978, the family moved to Suffolk in England, where Naomi attended Thomas Mills High School, but conceived the idea of becoming an actress after watching her mother performing on stage and from the time she watched the 1980 film Fame.

At the age of 14, she moved to Sydney, Australia, with her mother, brother and stepfather in 1982 and initially attended Mosman High School before changing to North Sydney Girls High School. However, she failed to graduate from school and signed with a modelling agency that sent her to Japan, but after several failed auditions, she returned to Sydney, where she tried several jobs, which included advertising for a department store and working as an assistant fashion editor of a magazine, named Follow Me. Finally, a casual invitation to participate in a drama workshop inspired Naomi to quit her job and follow her childhood interest in acting and after making brief appearances in television commercials, she made her big screen debut at the age of 18, appearing in a small role in an Australian romance, For Love Alone(1986). However, Naomi Watts had to wait for another five years to follow her debut screen presence, which mainly became possible for her fellow actress Nicole Kidman, whom she had befriended while they both auditioned for a bikini commercial and shared a taxi ride home. Kidman invited her at the premiere of her film Dead Calm and introduced her to director John Duigan, who invited her to take a supporting role in his boarding-school romance Flirting (1991), also starring Kidman and Thandie Newton.

After that, Naomi took a year off to travel and after appearing in a small role in John Goodman’s comedy film Matinee (1993), temporarily returned to Australia to star in three Australian films, which included another John Duigan's film Wide Sargasso Sea (1993), The Custodian (1993), a romantic drama directed by John Dingwall and George Miller’s thriller Gross Misconduct (1993), in which she appeared in her first leading role as Jennifer Carter, a student who accuses one of her teachers, played by Jimmy Smits, of raping her. After that, she moved back to America for good, but her initial efforts to find agents, producers and directors willing to hire her, made her frustrated. She even had to face the problems like being unable to pay the rent of her apartment and losing her medical insurance. Finally, she earned a supporting role, the role of Jet Girl after nine auditions, in the futuristic film Tank Girl (1995), based on a British comic strip, but although the film became something of a cult film, it failed to connect with audiences, met with mixed reviews and flopped at the box office. Throughout the rest of the decade, she got mostly supporting roles in films, appearing as Molly in the action-thriller Persons Unknown (1996), as Louise in the Australian ensemble romantic drama Under the Lighthouse Dancing (1997), as Giulia De Lezze in Dangerous Beauty (1998) and as Alice in the romantic comedy Strange Planet (1999).

However, despite working steadily in films and television projects, success eluded Naomi Watts, until David Lynch cast her in the starring Mulholland Drive (2001), originally intended as a television series. Lynch shot a large portion of it in February 1999, conceived as a pilot for the series, but the pilot was rejected, instead, Lynch filmed an ending in October 2000, turning it into a feature film. Premiered at the 2001 Cannes Film Festival, the film earned high critical acclaim and marked the breakthrough for Naomi Watts. Although the surrealist film, depicting the story of an aspiring actress, named Betty Elms, played by Watts, sparked controversy over its strong lesbian theme, Naomi was profusely acclaimed for her performance in the film and it was also maintained by some that she was overlooked for an Oscar nomination that year. However, the film received a large number of awards and nominations, including the Best Actress Award for Watts from the National Society of Film Critics and a nomination for Best Actress from the American Film Institute.

Nevertheless, Naomi Watts achieved stardom for her performance in The Ring (2002), the English language remake of a Japanese horror film, in which she portrayed the role of Rachel Keller, an investigating journalist, trying to find out the truth behind the strange death of her niece and other teenagers after watching a mysterious videotape and receiving a phone call announcing their deaths in seven days. Although the film did not fare well with the critics, it grossed around US$129 million domestically and launched Naomi into the spotlight. She then teamed with Heath Ledger for a remake of the Australian western Ned Kelly (2003) and also starred in Le Divorce (2003), a drama by James Ivory and Ismail Merchant, which failed miserably in the box office. However, she bounced back in 21 Grams (2003), directed by Alejandro Gonzalez Inarritu, in which she portrayed Cristina Peck, a grief-stricken woman living a suburban life after the brutal murder of her husband and two children and subsequently became involved in a relationship with the critically ill academic mathematician Paul Rivers, played by Sean Penn. For the portrayal of the character in the film, Naomi earned numerous award nominations, including an Academy Award nomination for Best Actress and brought others to call her one of the best in her generation of actors.

Naomi Watts headlined the remake of King Kong (2005) by Peter Jackson, in which she played leading lady Ann Darrow, portrayed by Fay Wray in the original version of the film in 1933. It was a huge project and it held the record for being the most expensive ever made in the States, until it was topped by Superman Returns in 2006. During the filming, Naomi had a horrific fall on the set in New Zealand, when she fell from a height into a ditch, to the shock of the cast and crew, but without any major harm. However, the film proved to be one of her most commercially successful films in the end. She then starred in The Painted Veil (2006) to play Kitty Fane, married to an intelligent, shy, somewhat dull and bookish physician, but becoming involved in an extramarital affair with a dashing, witty and married diplomat. While it was the second remake of the 1934 film with Greta Garbo playing the role of Kitty, Naomi Watts proved herself in every bit as good as Garbo was in the role, even her Kitty was acclaimed as more desperate, more foolish, more miserable and her spiritual journey is greater.

Her other important films during the decade include the thriller Eastern Promises (2007), directed by David Cronenberg, in which she portrayed a Russian-British midwife who delivers the baby of a drug-addicted 14-year-old prostitute; German director Michael Haneke’s Funny Games (2007), an English remake of his excruciatingly tense thriller, in which Naomi starred as a mother who, along with her family, is held hostage by a pair of sociopathic teenagers; and the political action thriller The International (2007), directed by the German film director Tom Tykwer, in which she played the role of Eleanor Whitman, the assistant district attorney, who joins an Interpol agent to uncover illegal activities to bring to justice one of the world's most powerful banks.

Naomi Watts appeared as Maria Bennett in The Impossible (2012), a fact-based disaster drama, in which María Belón faced the horrible experience of the 2004 Indian Ocean tsunami, along with her family. While the film was a critical darling and a huge box office success, Naomi Watt was profusely acclaimed for her performance, whose tears of pain and fear never appeared fake or idealized, earning nominations for Academy Award, Golden Globe Award and Screen Actors Guild Award for Best Actress. In 2014, she appeared as the actress of a play mounted by a faded Hollywood actor, played by Michael Keaton in Alejandro Gonzalez Inarritu’s dark comedy Birdman or the Unexpected Virtue of Ignorance (2014). The film won four Academy Awards, while Naomi Watts and the other cast members earned the Screen Actors Guild Award. Her subsequent important films include Demolition (2015), about a woman who becomes involved with a widower and The Glass Castle (2017), a drama about a dysfunctional family.

In her personal life, Naomi Watts never married, but had a relationship with Australian actor Heath Ledge from August 2002 to May 2004. After that, she began a relationship with American actor Isaac Liev Schreiber, with whom she appeared in The Painted Veil. After having two sons together in 2007 and 2008, they announced their split on 26 September 2016, after eleven years of togetherness. Since 2017, Naomi has been dating Billy Crudup, whom she met on the set of the Netflix drama series Gypsy and they made their red-carpet debut as a couple at the Screen Actors Guild Awards in February 2022.