Gary Crosby was born in Los Angeles and graduated from Stanford University. He entered the entertainment business and performed in a harmony singing group, The Crosby Boys, with his three brothers, Philip, Lindsay, and Dennis, during the 1940s, 1950s, and 1960s. As a teenager, he duetted with his father on two songs, "Sam's Song" and "Play a Simple Melody", which became the first double-sided gold record in history. He also recorded duets with Louis Armstrong and at least one 45-single with Sammy Davis Jr.. He also performed on several variety programs, including ABC's The Pat Boone Chevy Showroom and NBC's The Ford Show, Starring Tennessee Ernie Ford.
In the mid-1950s, he had his own radio program, the Gary Crosby Show on CBS. The musical variety program debuted June 6, 1954, as a summer replacement for Bing Crosby's show.
As an actor, Crosby appeared in many television programs. On March 20, 1955 he appeared on the Jack Benny Program Season 5, Episode 13. Later, he was briefly under contract to 20th Century-Fox in the late 1950s. He appeared in a number of supporting roles for the studio, normally comedies in which Crosby played a soldier: Mardi Gras (1958) with Pat Boone; Holiday for Lovers (1959), as Carol Lynley's love interest; A Private's Affair (1959), with Sal Mineo; The Right Approach (1961) with Frankie Vaughan.
He is perhaps best-remembered for his recurring roles as Eddie the scheming bellhop on The Bill Dana Show and Officer Edward "Ed" Wells on NBC's Adam-12 from 1968–75, as well as appearances on several other shows produced by Jack Webb's Mark VII Limited (including an episode of Dragnet 1969 and five episodes of Emergency!).. In addition to the aforementioned, he also appeared in three episodes of The Rockford Files.
In 1965, he made a guest appearance on Perry Mason as singer Jazbo Williams in "The Case of the Frustrated Folk Singer". He appeared in Girl Happy (1965), starring Elvis Presley, with whom he had been stationed in the Army, in Germany, and in "Come Wander with Me," an episode of The Twilight Zone in 1964. In the 1970s, he appeared occasionally on game shows such as Match Game and Tattletales as a guest panelist. He married and divorced three times; he had one stepchild as a result.