The Harlem-born Mineo and his family moved to the Bronx when he was nine years old, in part to escape the gangs with whom he was associating. One day while playing sandlot baseball with his sister and some friends, a talent scout "discovered" him. At the scout's encouragement, Mineo took dance lessons for several years and made his stage debut in Tennessee Williams' play "The Rose Tattoo" (1950), for which he earned $65 a week to utter the single line, "The goat is in the yard." This performance led to the job of understudy to the role of the crown prince in the Broadway musical "The King and I", starring Yul Brynner. After spending a year watching and waiting, Mineo was asked to assume the role when the original actor left the show. Just as Mineo's stage career was starting to take off, he decided to try his hand at film acting, playing small parts in "Six Bridges to Cross" opposite Tony Curtis and "The Private War of Major Benson" (both 1955) opposite Charlton Heston. Although he received good notices for both those performances, it was "Rebel Without a Cause", a film he made later that same year, that would launch his career and make his a household name. While the focus of the film was on Dean's character and his problems, it was Mineo's deft portrayal of Dean's frightened and vulnerable friend that many teens (even present day ones) found relatable. His outstanding performance earned him a Best Supporting Actor Oscar nomination and a small part in Dean's next big film "Giant" (1956). Despite the fact that "Giant" was a huge success, many of Mineo's fans were upset that he had a much smaller part than promoters led them to believe. They were also annoyed that the studio had a billed the film as a Dean/Mineo reunion when the actors didn't have any scenes together.
With Dean's sudden death in a car wreck at the age of 24, Mineo's popularity and fan base exploded, but quality roles failed to come his way. He starred as a teen thug in the movie "Crime in the Streets" (1956) and had a small role as Rocky Graziano's friend in the biopic "Somebody Up There Likes Me" (1957). Dean was originally set to play Graziano just before his death which Paul Newman later landed. Although Mineo deeply missed his friend, he reportedly said that he learned a lot working with Newman (another aficionado of "The Method") and was grateful for the experience.
After recreating his well-received small screen role of "Dino", a juvenile delinquent, in the 1957 feature film, Mineo starred in another biopic, playing the legendary, but troubled, jazz drummer in "The Gene Krupa Story" (1958). He earned his second Best Supporting Actor Oscar nomination for his performance in the Palestinian war for independence story "Exodus" (1960), which reteamed him with Newman. 1962 saw Mineo's career starting to slide as he appeared in poorly received movies like "Escape From Zahrain". Two years later, he was seen in the soft-core, low-budget thriller "Who Killed Teddy Bear?" (1964) a film critics have called everything from edgy to unwatchable. He followed up the sexy film with a small part in the Jesus drama "The Greatest Story Ever Told" in 1965.
With rumors regarding his sexuality swirling about Hollywood, Mineo found it increasingly difficult to find quality projects to work on. The solution, he decided, was to return to the stage. In 1965, Mineo made his directorial debut with "End as a Man" in an Ohio theater and went on to direct the controversial prison drama "Fortune and Men's Eyes" (1969), which starred a then-unknown Don Johnson. The controversial plays, although critically acclaimed, did not help Mineo's standing in Tinseltown and he appeared in his last movie "Escape From the Planet of the Apes" in 1971. At the time, he considered the job a fun one that would earn him some much-needed cash but the film, now considered by sci-fi fans as a classic, ended up being Mineo's celluloid swan song. In an effort to pay his ever-mounting bills, he increasingly turned to the small screen, acting in TV-movies ("The Family Rico", CBS 1972) and in episodes of the TV series like "S.W.A.T." and "Columbo".
In 1976, Mineo's career looked like it was going to take an upward turn as he enjoyed a successful run playing a bisexual burglar in the black comedy "P.S. Your Cat Is Dead" when it opened on stage in San Francisco. The popular show was in rehearsals for an L.A. production when Mineo was savagely stabbed to death outside of his apartment building. Although a man was tried and convicted of the murder, Mineo's family and friends have maintained that the police nabbed the wrong person and that his killer may still be at large.