On September 1, 1948, after a string of successful films for RKO, he and actress Lila Leeds were arrested for possession of marijuana. The arrest was the result of a sting operation designed to capture other Hollywood partiers as well, but Mitchum and Leeds did not receive the tip-off. After serving a week at the county jail, Mitchum spent 43 days (February 16 to March 30) at a Castaic, California, prison farm, with Life magazine photographers right there snapping photos of him mopping up in his prison uniform. The arrest became the inspiration for the exploitation film She Shoulda Said No! (1949), which starred Leeds. The arrest did little to affect Mitchum's career in the long term, but was seen as an embarrassment by his studio, who ordered Mitchum to clean up his act. The conviction was later overturned by the Los Angeles court and District Attorney's office on January 31, 1951, with the following statement, after it was exposed as a set-up:
"After an exhaustive investigation of the evidence and testimony presented at the trial, the court orders that the verdict of guilty be set aside and that a plea of not guilty be entered and that the information or complaint be dismissed."
Despite troubles with the law and his studio, the films released immediately after his arrest were box-office hits. Rachel and the Stranger (1948) featured Mitchum in a supporting role as a mountain man interested in gaining the hand of Loretta Young, the indentured servant and wife of William Holden, while the film adaptation of John Steinbeck's novella The Red Pony allowed him to portray a trusted cowhand to a ranching family.
Mitchum returned to true film noir in 1949's The Big Steal, where he again joined Jane Greer in an early Don Siegel film.
In Where Danger Lives (1950) he played a doctor who comes between a mentally unbalanced Faith Domergue and cuckolded Claude Rains. The Racket was a noir remake of the early crime drama The Racket and featured Mitchum as a police captain fighting corruption in his precinct. The Josef von Sternberg film Macao (1952) saw Mitchum a victim of mistaken identity at an exotic resort casino, playing opposite Jane Russell. Otto Preminger's Angel Face was the first of three collaborations between Mitchum and British stage actress Jean Simmons. In the film, Simmons plays an insane heiress who plans to use young ambulance driver Mitchum to kill for her.
Mitchum's cynical, mischievous attitude continued through adulthood and led him to shrug off fame as a fluke. On the set, he often played pranks on fellow actors and crew. His expulsion from 1955's Blood Alley is frequently attributed to his pranks, especially one in which he reportedly threw the film's transportation manager into San Francisco Bay. According to Sam O'Steen's memoir, "Cut to the Chase," Mitchum showed up on set after a night of drinking and tore apart a studio office when they didn't have a car ready for him. Mitchum walked off the set of the third day of filming Blood Alley, claiming he could not work with the director. Because he was showing up late and behaving erratically, producer John Wayne, after failing to obtain Humphrey Bogart as a replacement, took over the role himself.
Though Mitchum continued to star in a number of crime dramas, some classified within the film noir genre, 1955 marked his last true noir outing and his first film as a freelance actor, the Charles Laughton helmed The Night of the Hunter. Many considered this to be Mitchum's best performance. Following a series of conventional westerns and films noir, including the Marilyn Monroe vehicle River of No Return (1954), The Night of the Hunter would become one of the landmark films of the decade. Based on a novel by Davis Grubb, the film noir thriller starred Mitchum as a psychotic criminal posing as a preacher to find money hidden by his cellmate in the cellmate's home. The film remains one of the most chilling and suspenseful thrillers of the decade, though it was a critical and commercial failure upon its first release. While The Night of the Hunter was a box office flop which went on to become critically acclaimed decades afterward, Stanley Kramer's melodrama Not as a Stranger, also released in 1955, was a box office hit for Mitchum, which has been largely forgotten today. The film starred Mitchum against type, as an idealistic young doctor, who marries an older nurse (Olivia de Havilland), only to question his morality many years later. However, the film was not critically acclaimed, especially since Mitchum, Frank Sinatra and Lee Marvin were all too old for their characters.
Following a succession of average westerns and the poorly received Foreign Intrigue (1956), Mitchum starred in the first of three screen collaborations with British actress Deborah Kerr. The intriguing John Huston war drama Heaven Knows, Mr. Allison starred Mitchum as a marine corporal shipwrecked on a Pacific Island only to discover his sole companion is a nun, Sister Angela (Kerr). The character study centers on the relationship between the two as they fight for survival from the elements and the invading Japanese army. The film was nominated for two Academy Awards, including Best Actress and Best Adapted Screenplay. For his role, Mitchum was nominated for a BAFTA Award for Best Foreign Actor. Mitchum and Kerr were paired again in 1960, first for the critically acclaimed Fred Zinnemann film, The Sundowners, where they played husband and wife struggling in Depression-era Australia. Opposite Mitchum, Kerr was nominated for yet another Academy Award for Best Actress, while the film was nominated for a total of five Oscars. Robert Mitchum was awarded that year's National Board of Review award for Best Actor for his performance. The award also recognized his superior performance in the Vincente Minnelli western drama Home from the Hill. He was teamed with both Kerr and previous leading lady Jean Simmons as well as Cary Grant for the extremely offbeat Stanley Donen ensemble comedy The Grass Is Greener the same year.
Mitchum's performance as the menacing southern rapist Max Cady in 1962's Cape Fear brought him even more attention and furthered his renown as playing cool, predatory characters. The 1960s were marked by a number of lesser films and missed opportunities. Among the films Mitchum passed on during the decade was John Huston's The Misfits, the last film of its stars Clark Gable and Marilyn Monroe, the Academy Award-winning Patton, and Clint Eastwood's breakthrough film Dirty Harry. The most notable of his films later in the decade included the war epics The Longest Day (1962) and Anzio (1968), the Shirley MacLaine comedy-musical What a Way to Go! (1964), and the Howard Hawks western El Dorado (1966), a remake of Rio Bravo (1959), in which Mitchum took over Dean Martin's role of the drunk who comes to the aid of John Wayne.
One of the lesser known aspects of Mitchum's career was his forays into music, both as singer and composer.
Mitchum's voice was often used instead of that of a professional singer when his characters sang in his films. Notable productions featuring Mitchum's own singing voice included Rachel and the Stranger, River of No Return and The Night of the Hunter. After hearing traditional calypso music and meeting artists such as Mighty Sparrow and Lord Invader while filming Heaven Knows, Mr. Allison in the Caribbean island of Tobago, he recorded Calypso — Is Like So... in March 1957. On the album, released through Capitol Records, he emulated the calypso sound and style, even adopting the style's unique pronunciations and slang. A year later he recorded a song he had written for the film Thunder Road, titled "The Ballad of Thunder Road." The country-styled song became a modest hit for Mitchum, reaching #69 on the Billboard Pop Singles Chart. The song was included as a bonus track on a successful reissue of Calypso... and helped market the film to a wider audience.
Though Mitchum continued to use his singing voice in his film work, he waited until 1967 to record his follow-up record, That Man, Robert Mitchum, Sings. The album, released by Nashville-based Monument Records, took him further into country music, and featured songs similar to The Ballad of Thunder Road. "Little Old Wine Drinker Me," the first single, was a top ten hit at country radio, reaching #9 there, and crossed over onto mainstream radio, where it peaked at #96. Its follow-up, "You Deserve Each Other," also charted on the Billboard Country Singles Chart.
Mitchum also co-wrote and composed the music for an oratorio which was produced by Orson Welles at the Hollywood Bowl.
Mitchum made a departure from his typical screen persona with the 1970 David Lean film Ryan's Daughter, in which he starred as Charles Shaughnessy, a mild-mannered schoolmaster in World War I era Ireland. Though the film was nominated for four Academy Awards (winning two) and Mitchum was much publicized as a contender for a Best Actor nomination, he was not nominated. George C. Scott won the award for his performance in Patton, a project which Mitchum had rejected for Ryan's Daughter.