Born Laura Augusta Gainor in Philadelphia, Pennsylvania, her family moved west to San Francisco when she was just a child. When graduated from high school in 1923, Gaynor decided to pursue a career in acting. She then moved to Los Angeles, where she supported herself working in a shoe store, receiving $18 per week. She managed to land unbilled small parts in several feature films and comedy shorts for two years.
Finally, in 1926, at the age of 20, she was cast in the lead role in a silent film called The Johnstown Flood, the same year she was selected as one of the WAMPAS Baby Stars (with Joan Crawford, Dolores del Rio and others). Her outstanding performance won her the attention of producers, who cast her in a series of films.
Within one year, Gaynor was one of Hollywood's leading actresses. Her performances in Seventh Heaven, Sunrise and Street Angel earned her the first Academy Award for Best Actress in 1928. It was the only time in Oscar history that the award was given for multiple roles: it was given on the basis of the actor's total work over the year, and not just for one particular performance.
Gaynor was one of only a handful of leading ladies who made a successful transition to sound movies over the next decade. And for a number of years, Gaynor was the leading actress of the Fox studios and was treated accordingly with top billing and the choice of prime roles, starring in such films as Delicious, Adorable, and Merely Mary Ann.
However, when Darryl F. Zanuck merged his fledgling studio, 20th Century Pictures, with Fox Film Corporation to form Twentieth Century Fox, her status became precarious and even tertiary to that of actresses Loretta Young and Shirley Temple. She managed to terminate her contract with the studio and achieved acclaim in films produced by David O. Selznick in the mid-1930s.
In 1937, she was again nominated for an Academy Award, this time for her role in A Star Is Born. After appearing in The Young in Heart, she left film industry for nearly twenty years, returning one last time in 1957 as Pat Boone's mother in Bernardine.
Gaynor was married to producer Paul Gregory from 24 December 1964 to her death. Previous marriages were to MGM costume designer Adrian from 14 August 1939 to his death on 13 September 1959, and to Jesse Lydell Peck from 11 September 1929 to 7 April 1933. Gaynor had one son with Adrian, Robin Gaynor Adrian, born in 1940.
Janet Gaynor was a bisexual whose early strategy was to divert fan mag questions about her romantic life to discussions of her work. This was less necessary when she was married. Between marriages, and sometimes during them, she apparently had reasons to be discreet that went beyond simply her well-known penchant for privacy.
William Mann's meticulously researched book Behind the Screen: How Gays and Lesbians Shaped Hollywood 1910-1969 says that Gaynor was a lifelong lesbian, seriously involved with at least two other stars, Margaret Livingston and, most significantly, Mary Martin.
Gaynor was indeed close friends with actress Mary Martin, with whom she frequently travelled. A Brazilian press report noted that Gaynor and Martin briefly lived with their respective husbands in the state of Goiás in the 1950s and 1960s. Actor Robert Cummings once quipped: "Janet Gaynor's husband was Adrian, the MGM fashion designer. But her wife was Mary Martin."
She died at the age of 77, due largely to the aftermath of a traffic accident in San Francisco two years earlier. In the accident, a driver named Robert Cato ran a red light at the corner of California Street and Franklin and crashed into her Luxor taxicab. The violent crash killed Mary Martin's manager Ben Washer and injured the other passengers, including Gaynor's husband Paul Gregory, as well as her close, long-time friend, Mary Martin.
Gaynor was in serious condition with eleven broken ribs, a fractured collarbone, pelvic fractures, an injured bladder and a damaged kidney. She never fully recovered from the accident and after several operations died of complications.
She was interred in the Hollywood Forever Cemetery in Hollywood, California next to her second husband Adrian, but her stone reads "Janet Gaynor Gregory" in tribute to her third husband, producer and director Paul Gregory.