Cooper was born in Helena, Montana, one of two sons of an English immigrant couple, Alice (née Brazier; 1873–1967) and Charles Henry Cooper (1865–1946). His father was a farmer from Houghton Regis, Bedfordshire, who later became an American lawyer and judge, and his mother was from Kent. His mother hoped for their two sons to receive a better education than was available in Montana and arranged for the boys to attend Dunstable Grammar School in Bedfordshire, England, between 1910 and 1913. Following the outbreak of World War I, Cooper's mother brought her sons home and enrolled them at Gallatin Valley High School in Bozeman, Montana.
When Cooper was 13, he injured his hip in a car accident. He returned to his parents' ranch near Helena to recuperate by horseback riding at the recommendation of his doctor. Cooper studied at Iowa's Grinnell College until the spring of 1924, but did not graduate. He had tried out, unsuccessfully, for the college's drama club. He returned to Helena, managing the ranch and contributing cartoons to the local newspaper. In 1924, Cooper's father left the Montana Supreme Court bench and moved with his wife to Los Angeles. Their son, unable to make a living as an editorial cartoonist in Helena, joined them, moving there that same year, reasoning that he "would rather starve where it was warm, than to starve and freeze too."
Unsuccessful as a salesman of electric signs and theatrical curtains, as a promoter for a local photographer, and as an applicant for newspaper work in Los Angeles, Cooper found work as an actor in 1925. Beginning as an extra in the motion picture industry, usually being cast as a cowboy, he is known to have had an uncredited role in the Tom Mix Western Dick Turpin (1925). The following year, he received a screen credit in a two-reeler, Lightnin' Wins, with actress Eileen Sedgwick as his leading lady.
After the release of this short film, Cooper accepted a long-term contract with Paramount. He changed his name to Gary in 1925, following the advice of casting director Nan Collins, who felt it evoked the "rough, tough" nature of her native Gary, Indiana.
"Coop," as he was called by his peers, went on to appear in over 100 films. With help from established silent star Clara Bow, Cooper broke through in a supporting role in the late silent Wings (1927), the first film to win an Academy Award for Best Picture, following it with Nevada (1927) co-starring Thelma Todd and William Powell, based on the Zane Gray novel. (This was remade as an early Robert Mitchum vehicle released in 1944, the only time Cooper and Mitchum played the same role.) Cooper became a major star with his first sound picture, The Virginian (1929) which features Walter Huston as the villainous Trampas. The Spoilers appeared the following year with Betty Compson (which was remade in 1942 with Marlene Dietrich, who resembled Compson, and John Wayne in Cooper's role). Cooper followed this action film with Morocco (1930), starring Dietrich, in which he played a Foreign Legionnaire. Devil and the Deep(1932) featured Cary Grant in a supporting role with Talullah Bankhead and Cooper in the leads alongside Charles Laughton. The following year, Cooper was the second lead in the sophisticated Ernst Lubitsch comedy production of Noël Coward's Design for Living. He was billed under Fredric March in the kind of fast-talking role Cooper never played again after Cary Grant staked out the light comedy leading man field with The Awful Truth four years later. The screen adaptation of A Farewell to Arms (1932), directed by Frank Borzage, and the title role in Frank Capra's Mr. Deeds Goes to Town (1936) furthered Cooper's box-office appeal.
Cooper was producer David O. Selznick's first choice for the role of Rhett Butler in Gone with the Wind. (1939). When Cooper turned down the role, he was passionately against it. He is quoted as saying, "Gone with the Wind is going to be the biggest flop in Hollywood history. I’m glad it’ll be Clark Gable who’s falling flat on his nose, not me". Alfred Hitchcock wanted him to star in Foreign Correspondent (1940) and Saboteur(1942). Cooper later admitted he had made a "mistake" in turning down the director. For the former film, Hitchcock cast look-alike Joel McCreainstead.
Cooper cemented his cowboy credentials again in The Westerner (1940), with Walter Brennan as Judge Roy Bean, and followed that immediately afterward with the lavish North West Mounted Police(1940), directed by Cecil B. DeMille and featuring Paulette Goddard.
Cooper won his first Academy Award for Best Actor in 1942 for his performance as the title character in Sergeant York (1941). It often has been rumored that Alvin York refused to authorize a movie about his life unless Cooper portrayed him. Evidence has since surfaced that the film's producer, Jesse L. Lasky, sent a telegram pleading with Cooper to take the part and signed York's name to it. Meet John Doe had been released earlier in 1941, a great success under the direction of Frank Capra. Cooper worked with Ingrid Bergman in For Whom the Bell Tolls (1943), directed by Sam Wood and based on a novel by Cooper's close friend Ernest Hemingway; they spent many vacations in Sun Valley, Idaho together. A Western comedy lampooning his hesitant speech and mannerisms and his own image in general followed called Along Came Jones (1945) in which he relied on gunslinging Loretta Young to save him. Cooper also starred with Patricia Neal in the original screen adaptation of the Ayn Rand novel The Fountainhead (1949).
Cooper won his second Best Actor Academy Award for his performance as Marshal Will Kane in High Noon (1952), sometimes thought his finest role. Ill with an ulcer and busy filming Blowing Wild (1953) in Mexico, he wasn't present to receive his Academy Award in February 1953. He asked John Wayne to accept it on his behalf, a bit of irony in light of Wayne's stated distaste for the film. The following year Cooper was filmed reading the list of nominees for the Best Actress award which went to Audrey Hepburn.
Cooper continued to play the lead in films almost to the end of his life. Among his later box office hits were the stark Western adventure Garden of Evil (1954) with Susan Hayward and Richard Widmark; Vera Cruz (1954), an extremely influential Western in which he guns down villain Burt Lancaster in a showdown; his portrayal of a Quaker farmer during the American Civil War in William Wyler's Friendly Persuasion (1956); Billy Wilder's Love in the Afternoon (1957) with Audrey Hepburn; and Anthony Mann's Man of the West (1958), a hard-edged action Western with Lee J. Cobb. His final motion picture was a British film, The Naked Edge (1961), made in London in the autumn of 1960. His final project was narrating an NBC documentary, The Real West, in which he helped clear up myths about legendary Western figures.
Cooper had several high-profile relationships with actresses Clara Bow, Lupe Vélez, and the American-born socialite-spy, Countess Carla Dentice di Frasso (née Dorothy Caldwell Taylor, former wife of British pioneer aviator Claude Grahame-White).
On December 15, 1933, Cooper married Veronica Balfe, aka 'Rocky'. Balfe was a New York, Roman Catholic socialite who briefly had acted under the name of Sandra Shaw. She appeared in the film No Other Woman, but her most widely seen role was in King Kong(1933), as the woman dropped by Kong. Her third and final film was Blood Money (also 1933). Her stepfather was governor of the New York Stock Exchange, and her uncle was motion-picture art director Cedric Gibbons. During the 1930s she also became the California state women's skeet shooting champion. Cooper and Balfe had one child, Maria, in 1937, who later married classical pianist, Byron Janis.
After Cooper was married, but prior to his conversion to Catholicism, he had affairs with several famous co-stars, including Marlene Dietrich, Grace Kelly and Patricia Neal. Cooper and Neal began their affair after meeting on the set of The Fountainhead. The relationship eventually became an open secret in Hollywood. Cooper's wife, Rocky, confronted him with the rumors which he admitted were true and also confessed that he was in love with Neal. Rocky later told the couple's daughter, Maria, of the affair; she blamed Neal. The next time Maria saw Neal, she angrily spat on the ground in front of Neal. Cooper and his wife kept up a front of a happy marriage, but Cooper continued to see Neal. In 1950 Neal discovered she was pregnant. Cooper arranged and paid for her to have an abortion to avoid the public scandal of having a child out of wedlock. Cooper and his wife separated that same year. Cooper and Neal continued to see each other, but Cooper was hesitant to divorce Rocky, fearing he would lose the respect of his daughter, Maria. Neal finally ended the affair in late 1951. Cooper, however, would not reunite with his wife until 1954. A year later he had an affair with Anita Ekberg.
In April 1960 Cooper underwent surgery for prostate cancer after it had spread to his colon. It spread to his lungs and bones shortly thereafter. Cooper, however, was not informed his cancer was terminal until February 1961.
Cooper was too ill to attend the Academy Awards ceremony in April 1961, so his close friend, James Stewart, accepted the honorary Oscar on his behalf. Stewart's emotional speech hinted that something was seriously wrong, and the next day newspapers ran the headline, "Gary Cooper has cancer". One month later on May 13, 1961, six days after his 60th birthday, Cooper died.
Cooper was originally interred in Holy Cross Catholic Cemetery in Culver City, California. In May 1974 his body was removed from the Grotto Section of Holy Cross Cemetery, when his widow Veronica remarried and moved to New York. She had Cooper's body exhumed and reburied in Sacred Heart Cemetery in Southampton, New York, on Long Island.Veronica "Rocky" Cooper-Converse died in 2000 and was buried near Cooper at Sacred Heart Cemetery.