Since Darnell was underage when she arrived in Hollywood, she was tutored on the sets. She planned on attending graduation day at Sunset High School, but she was excluded from it, and instead she graduated from University High School in 1941.:66 Her work schedules prohibited her from enrolling in a university.
In 1940, during the shooting of Star Dust, Darnell for a short time went out with teen idol Mickey Rooney.:53 Her first love was Jaime Jorba, a Mexican whom she met while still in high school. They met again during production of Blood and Sand, but they drifted apart when Jorba announced he could not marry a girl who was in the public eye.:62 Starting at age 17, Darnell dated her publicity agent Alan Gordon, whom she allegedly married in a double wedding with Lana Turner and Joseph Stephen Crane on July 17, 1942. The report turned out to be false, and over the years Darnell became known as "filmland's most eligible bachelorette.":72 Up to 1942, she dated Kay Kyser, Eddie Albert, George Montgomery and Jackie Cooper, among others.:72 At one point, she was set to elope with talent agent Vic Orsatti, only to report later that she was "concentrating on [her] career.":72
Although a well-loved figure on the 20th Century Fox lot among the cast, crew and lot workers, it was reported that Darnell made only one good friend in Hollywood, actress-singer Ann Miller, whom she met at a Catalina Island benefit.:58 Darnell was very negative about the Hollywood social scene, finding it "nauseating".:69 During her stay in Hollywood, her relationship with her mother Pearl worsened, her mother being an unpopular figure on the lot due to her overbearing and possessive behavior.:60 In 1940, Pearl accused her husband of having an incestuous relationship with Evelyn, one of her children, even though he was not Evelyn's biological father.:55 Following an intense fight between her parents in 1942, Darnell left home with her younger sister Monte and never returned.:71 In spite, Pearl turned to the press, which gained Darnell some bad publicity.
In 1942, Darnell was plagued with extortion letters from an unknown person threatening her with bodily harm unless $2,000 was paid immediately. The studio asked the FBI to protect the actress, and eventually a 17-year-old high school student was arrested for the crime.:70–71
On April 18, 1943, at age 19, Darnell eloped with 42-year-old cameraman J. Peverell Marley in Las Vegas. Darnell and Marley started seeing each other in 1940, and the press dismissed him as her "devoted friend and escort.":54 Most friends and relatives disapproved of the marriage, including 20th Century Fox and her parents, and it was believed that Darnell looked at Marley more as a father figure than her romantic interest.:77 Marley was a heavy drinker and introduced Darnell to alcohol in 1944, which eventually led to an addiction and weight problem.:84–85 Neighbors and acquaintances recalled the drastic change she underwent in this period, becoming hardened and hot-tempered. In 1946, during production of Centennial Summer, she repeatedly met with Howard Hughes. Although she initially disregarded gossip of an affair, she fell in love with the womanizing millionaire and separated from Marley shortly after finishing My Darling Clementine.:93–94 When Hughes announced that he had no desire to marry her, Darnell returned to her husband and cancelled divorce proceedings. Shortly after the reunion, her health worsened, caused by the tough production of Forever Amber (1947).
Because Darnell and Marley were unable to have children, they adopted a daughter in 1948, Charlotte Mildred "Lola" Marley (born January 5, 1948), the actress's only child. She also planned to adopt a boy within years, but nothing ever came of it.:107 In mid-1948, she became romantically involved with Joseph L. Mankiewicz, the director of A Letter to Three Wives, and in July 1948, she filed for divorce. Mankiewicz, however, was unwilling to leave his wife for Darnell, and even though the affair would continue for six years, she returned to her husband. Whereas she called him the "great love of her life," Mankiewicz never acknowledged the affair; he only mentioned her to his biographer as a "marvelous girl with very terrifying personal problems.":112 In 1949, Darnell went into psychotherapy for hostile emotions that she had been building since childhood.:114 Darnell's romance with Mankiewicz influenced her personal life. When he left in late 1949 for on location shooting of All About Eve (1950), Darnell fell into a depression and almost committed suicide.:117 She continued to occasionally meet with him until production of The Barefoot Contessa (1954) started.
On January 25, 1949, Darnell went to court to sue her former business manager Cy Tanner for fraud. She testified that he stole $7,250 from her between 1946 and 1947, and Tanner was eventually sent to prison.:115 On July 19, 1950, it was reported that Darnell had separated from her husband. Marley offered a quiet settlement - without mention of Mankiewicz - for a payment of $125,000. She agreed, and she almost lost all of her money. When she filed for divorce from Marley in 1951, she accused her husband of cruelty, claiming he was "rude" and "critical" towards Darnell and her family. Following a five-minute hearing, Darnell was granted a divorce and custody of Charlotte, while Marley was to pay $75 a month for child support.
In her later life, she dated actor Dick Paxton and had an affair with Italian director Giuseppe Amato.:137 She secretly married brewery heir Philip Liebmann in February 1954. Due to a lack of physical attraction from her side, Darnell agreed that the marriage would be a business arrangement: she was to be his wife in name only, and in return, he supported her financially.:140 After a while, she grew dissatisfied with her loveless marriage, and she detested her husband for allowing her to lash out at him, as well as cheapening her by buying her lavish presents.:141 In response, Darnell resorted to charity work, opening facilities accommodating thirty girls in the neighborhood of Rome in 1955. Liebmann attempted to save the marriage by adopting a baby named Alfreda, but the marriage ended nevertheless on grounds of incompatibility, and Liebmann kept the girl.:146
Darnell was married to pilot Merle Roy Robertson from 1957 to 1963. In 1963, Darnell was granted a divorce from Robertson following an outburst in the courtroom, where she accused her third husband of fathering the baby of a Polish actress. She was promised a monthly alimony of $350 until July 15, 1964, and $250 until September 15, 1967.
She died on April 10, 1965, at age 41, from burns she received in a house fire in Glenview, Illinois. She had been staying there with friends while preparing for a stage role in the Chicagoarea. Her 1940 film, Star Dust, had played on television the night of the fire, and it was widely reported that Darnell had fallen asleep with a lit cigarette while watching it. Some more sensational reports claimed she was intoxicated and despondent over her career. But biographer Ronald L. Davis, in his book Hollywood Beauty, wrote that there was no evidence that any of these stories were true, or that Darnell was in any way responsible for the blaze. By his account, Darnell was burned over 90 percent of her body because rather than jump from the window as her friend's daughter had already done, Darnell tried to make it to the front door. She reached the door but the doorknob was too hot to touch.:177–179
Her ashes are interred at the Union Hill Cemetery, Chester County, Pennsylvania, in the family plot of her son-in-law. For her contribution to the motion picture industry, Linda Darnell has a star on the Hollywood Walk of Fame at 1631 Vine Street.