Born in Oakland, California, Beckett got his start in show business at age 3 when the family moved to Los Angeles and a casting director heard him singing by chance. Beckett was in the Cedars of Lebanon Hospital visiting his father who was recovering from an illness, and was entertaining him by singing songs. Nurses who heard him singing and took him from room to room to sing for other patients. A studio casting director who happened to be nearby noticed the child, and told his parents he had movie potential. Beckett auditioned, and landed a part in Gallant Lady (1933), alongside Dickie Moore. The same year, his father died. In 1934, Beckett joined Our Gang, in which Moore had appeared from 1932 to 1933
Beckett appeared as a regular in the Our Gang short subjects series from 1934 to 1935. In the gang, Beckett played George "Spanky" McFarland's best friend and partner in mischief. His trademark look was a crooked baseball cap and an oversized sweater exposing one shoulder. His role was taken over by Carl "Alfalfa" Switzer in 1935, and Beckett left the series for features after that year.
Beckett became a prolific child and young adult actor from the late 1930s to the early 1950s. In 1939, he returned to Our Gang briefly as Alfalfa's cousin Wilbur in Cousin Wilbur and Dog Daze. He appeared as one of the unborn children in Shirley Temple's The Blue Bird (1940). He played Al Jolson as a teenager in The Jolson Story (1946), with his singing voice provided by Rudy Wissler. His performance as Jolson was described as "touching, enchanting, and to all indications, accurate".
After his Our Gang days were over, Beckett won increasingly prominent roles in major Hollywood films, usually playing the star's son or the hero as a boy. Among his major credits are Dante's Inferno with Spencer Tracy, Anthony Adverse with Fredric March, The Charge of the Light Brigade with Errol Flynn, Conquest with Greta Garbo, Marie Antoinette with Norma Shearer; Ali Baba and the Forty Thieves, where he played Jon Hall's character as a child and Kings Row, where he played Robert Cummings's character as a child. In 1940, he played Tim in My Favorite Wife, starring Cary Grant and Irene Dunne, the title character. He also had a central role in the wartime propaganda film The Boy from Stalingrad (1943).
Beckett attended Los Angeles High School and took time off from filming to try his luck on the stage. Adolescence didn't seem to hamper his career, as he won such important roles as that of young Al Jolson in The Jolson Story and Junior in the long-running radio show The Life of Riley. In 1947, he appeared alongside Dickie Moore and Marilyn Monroe in Dangerous Years.
Scotty Beckett was signed by MGM with his first role under contract as Will Parker in Cynthia. He gained the role of Oogie Pringle in A Date with Judy, the film adaptation of the long-running radio series of the same name, opposite Jane Powell as Judy Foster. In 1949, the actor was featured in the war drama Battleground and the following year he starred as the fast-talking Tennessee Shad in the MGM comedy The Happy Years. By 1950, the success of those three films, resulted in expectations that Beckett's career would rise, but it did not. While other actors his age moved into leading roles, his career declined, as evidenced by his small role in Nancy Goes to Rio, again with Jane Powell.
He attended the University of Southern California, but dropped out when the combined workload of school and movies became too great. Although he was working steadily at MGM, his life grew increasingly tumultuous in the late 1940s and early 1950s. In 1948 he was arrested on suspicion of drunk driving. The following year he eloped with Beverly Baker, a tennis star, but their marriage dissolved within a period of months. His second marriage with Sunny Vickers produced one son, Scott Jr. In 1954 Beckett ran afoul of the law again, once for passing a bad check and once for carrying a concealed weapon.
Ironically, that same year Beckett's career took an upward turn, as he was cast as Winky, the comic sidekick in the popular TV show Rocky Jones, Space Ranger. This was to be his last major role. He made only a few subsequent TV and film appearances, some uncredited bit parts, before leaving show business forever.
The last ten years of Beckett's life were filled with stories of divorce, violence, drugs and arrests. After more or less giving up show business, he tried selling real estate, then cars, and twice enrolled at universities with the intention of becoming a medical doctor. In 1961, Beckett married Margaret C. Sabo; she would remain with him until his death.
On May 8, 1968, he checked into a Hollywood nursing home, needing medical attention after suffering a serious beating. He died two days later at age 38. Although pills and a note were found, no conclusion was made by the coroner as to the exact cause of death; however, some speculate he overdosed on barbiturates or alcohol.
Leonard Maltin later wrote: "It was a particularly sad end for someone who, as a child, had shown so much easy charm and talent."