The only child of Helen Lita (née Westergaard) and Frederick Robert Morrison, Leigh was born as Jeanette Helen Morrison in Merced, California, and grew up in Stockton, California. In the winter of 1945, she was discovered by the actress Norma Shearer, whose late husband Irving Thalberg had been a senior executive at Metro-Goldwyn-Mayer. Shearer showed talent agent Lew Wasserman a photograph she had seen of Leigh while vacationing at Sugar Bowl, the ski resort where the girl's parents worked. Shearer later recalled that "that smile made it the most fascinating face I had seen in years. I felt I had to show that face to somebody at the studio.""'Luckiest' Photograph Changed Whole Life for a College Girl", Milwaukee Journal Sentinel, August 16, 1947, p. 1 Leigh left the University of the Pacific, where she was studying music and psychology, after Wasserman secured a contract with MGM, despite having no acting experience. She was placed under the tutelage of drama coach Lillian Burns.

Leigh made her film debut in the big budget film The Romance of Rosy Ridge in 1947, as the romantic interest of Van Johnson's character. She got the role when performing Phyllis Thaxter's long speech in Thirty Seconds Over Tokyo (1944) for the head of the studio talent department in 1946. During the shooting, Leigh's name was first changed to 'Jeanette Reames', then to 'Janet Leigh' and finally back to her birth name 'Jeanette Morrison', because 'Janet Leigh' resembled Vivien Leigh too much. However, Johnson did not like the name and it was finally changed back to 'Janet Leigh'. Leigh initially left college for a film career, but enrolled in night school at the University of Southern California in 1947.

Immediately after the film's release, Leigh was cast opposite Walter Pidgeon and Deborah Kerr in If Winter Comes (1947) in the summer of 1947. Furthermore, due to the box office success of The Romance of Rosy Ridge, Leigh and Johnson were teamed up again in a film project called The Life of Monty Stratton in August 1947. The project was eventually shelved and released in 1949 as The Stratton Story, starring James Stewart and June Allyson. Another film that Leigh was set to star in, before being replaced, was Alias a Gentleman, in which she was cast in April 1947. By late 1947, Leigh was occupied with the shooting of the Lassie film Hills of Home (1948), the first film in which she received star billing.

In late 1948, Leigh was hailed the 'No. 1 glamor girl' of Hollywood, although known for her polite, generous and down-to-earth persona.

Many movies followed, notably the title role in the musical comedy My Sister Eileen, co-starring Jack Lemmon, Betty Garrett and Dick York. She proved versatile, starring in films as diverse as the baseball farce Angels in the Outfield in 1951 and the tense western The Naked Spur in 1953.

Her initial roles were ingenues based on characters from historical literature, for example in Scaramouche opposite Stewart Granger. By 1958, she moved to more complex roles.

Leigh's best-known role was as the morally ambiguous Marion Crane in the Alfred Hitchcock film Psycho (1960), featuring its iconic shower murder scene. She received a Golden Globe Award for Best Supporting Actress and was nominated for the Academy Award for Best Supporting Actress.

Leigh had starring roles in many other films, including the Orson Welles film-noir classic Touch of Evil, 1962's The Manchurian Candidate with Frank Sinatra and the 1963 musical Bye Bye Birdie based on the hit Broadway show.

She co-starred with third husband Tony Curtis in five films, Houdini (1953), The Black Shield of Falworth (1954), The Vikings (1958), The Perfect Furlough (1959) and Who Was That Lady? (1960).

In 1975, Leigh played a retired Hollywood song and dance star opposite Peter Falk and John Payne in the Columbo episode Forgotten Lady. She also appeared in two horror films with her daughter, Jamie Lee Curtis, playing a major role in The Fog (1980), and making a brief appearance in 20 Years Later (1998).

Leigh is also the author of four books. Her first, the memoir "There Really Was a Hollywood", was a NY Times bestseller. This was followed by the novels "House of Destiny" and "The Dream Factory", and the non-fiction book "Psycho: Behind the Scenes of the Classic Thriller". Interestingly, daughter Jamie Lee Curtis is also an actress and popular author.

At the age of 16, Janet Leigh married John Kenneth Carlisle in 1943. The marriage was annulled the same year. She married Stanley Reames in 1946 and they were divorced in 1948.

Leigh married her third husband, Tony Curtis, on June 4, 1951. They had two children, Kelly and Jamie Lee, both who subsequently became actresses. Following their divorce in 1962, Leigh married stockbroker Robert Brandt in Las Vegas. They remained married until her death.

She served on the board of directors of the Motion Picture and Television Foundation, a medical-services provider for actors.

Leigh was awarded an honorary Doctor of Fine Arts degree at the University of the Pacific in Stockton, California on May 14, 2004.

Leigh died at her home on October 3, 2004, after suffering cardiac arrest. She suffered from vasculitis and peripheral neuropathy, which caused her right hand to become gangrenous.