Born Byron Elsworth Barr in St. Cloud, Minnesota, he and his older siblings were raised by his parents, John and Emma Barr, in Washington initially. When he was six, his family moved back to their hometown of Waynesville, North Carolina, where he was raised. He developed a passion for the theatre while appearing in high school plays, and after some amateur experience he applied for and received a scholarship to the acclaimed Pasadena Community Playhouse. While acting in Pancho, a south-of-the-border play by Lowell Barrington, he and the leading actor in the play, George Reeves, were spotted by a Warner Brothers talent scout. Both actors were signed to supporting player contracts with the studio. His early work was un-credited or as Byron Barr (not to be confused with another actor with the same name, Byron Barr).
After appearing in the 1942 film The Gay Sisters – written by Stephen Longstreet (1907–2002) – as a character named "Gig Young", the studio determined that "Gig Young" should become Barr's stage and professional name.
Young appeared in supporting roles in numerous films during the 1940s, and came to be regarded as a popular and likable second lead, playing the brothers or friends of the principal characters. Young took a hiatus from his movie career and enlisted in the United States Coast Guard in 1941 where he served as a pharmacist's mate until the end of World War II. In early 1942, in an uncredited bit part and nearly unseen, in his distinctive voice, he had one line, "How's the ice?", in the Bette Davis film The Man Who Came to Dinner. Less than two years later, he played opposite her as her much-younger beau in Old Acquaintance.
After Young's return from the war, Warner Bros. dropped his option. He then began freelancing at various studios, eventually obtaining a contract with Columbia Pictures before returning to freelancing. During those years, Young began to play the type of role that he would become best known for, a sardonic but engaging and affable drunk. His dramatic work as an alcoholic in the 1951 film Come Fill the Cup with James Cagney and his comedic role as a tipsy but ultimately charming intellectual in Teacher's Pet starring Clark Gable and Doris Day earned him nominations for Academy Award for Best Supporting Actor.
In 1955, Young became the host of Warner Bros. Presents, an umbrella title for three television series (Casablanca, Kings Row, and Cheyenne) that aired during the 1955–56 season on ABC Television. He played a supporting role the same year in the Humphrey Bogart thriller The Desperate Hours. Young is also remembered by many James Dean fans for the "driving safety" interview made shortly before Dean's fatal car accident in September, 1955. On the 1964–65 NBC series The Rogues, he shared appearances on a rotating basis with David Niven and Charles Boyer.
Young won the Academy Award for his role as Rocky, the dance marathon emcee and promoter in the 1969 film They Shoot Horses, Don't They? According to his fourth wife, Elaine Williams, "What he was aching for, as he walked up to collect his Oscar, was a role in his own movie—one that they could finally call 'a Gig Young movie.' For Young, the Oscar was literally the kiss of death, the end of the line". Young himself had said to Louella Parsons, after failing to win in 1951, "so many people who have been nominated for an Oscar have had bad luck afterwards."
After a substantial supporting role in Lovers and Other Strangers in 1970, alcoholism began to cost him roles. He collapsed on the set of the comedy film Blazing Saddles during his first day of shooting due to alcohol withdrawal, and was fired. Young's last role was in the 1978 film Game of Death, released nearly six years after the film's star, Bruce Lee, died during production in 1973.
Young was married five times; his first marriage to Sheila Stapler lasted seven years, ending in 1947. In 1950, he married Sophie Rosenstein, the resident drama coach at Paramount, who was several years Young's senior. She was soon diagnosed with cancer, and died just short of two years after the couple's wedding. After her death, Young was engaged to actress Elaine Stritch.
He met actress Elizabeth Montgomery after she appeared in an episode of Warner Bros. Presents in 1956, and the two married later that year. In 1963, Montgomery divorced Young because of his alcoholism.
Young married his fourth wife, real estate agent Elaine Williams, nine months after his divorce from Montgomery was final. Williams was pregnant with Young's child at the time and gave birth to his only child, Jennifer, in April 1964. After three years of marriage, the couple divorced. During a legal battle over child support with Williams, Young denied that Jennifer was his biological child. After five years of court battles, Young lost his case.
On September 27, 1978, Young, age 64, married his fifth wife, a 31-year-old German magazine editor named Kim Schmidt. He met Schmidt in Hong Kong while working on Game of Death.
On October 19, 1978, three weeks after his marriage to Schmidt, the couple were found dead at home in their Manhattan apartment. Police theorized that Young shot his wife and then turned the gun on himself. A motive for the murder-suicide was never made clear. Young was at one time under the care of the psychologist and psychotherapist Eugene Landy, who would later have his professional California medical license revoked amidst accusations of ethical violations and patient misconduct.
Young was buried in the Green Hill Cemetery in Waynesville, North Carolina in his family's plot along with his parents, siblings and an uncle. Young's will, which covered a $200,000 estate, left his Academy Award to his agent, Martin Baum and Baum's wife, Bernice; however, Young's daughter Jennifer launched a campaign in the early 1990s to get the award back from his agent, and struck an agreement that she would get the award back upon the agent's death, which occurred in 2010.
For his contribution to the television industry, Young has a star on the Hollywood Walk of Fame at 6821 Hollywood Boulevard.