Crawford was born in Los Angeles, California, the son of Betty (née Megerlin) and Robert Lawrence Crawford, Sr. His maternal grandparents were Belgian; his maternal grandfather was violinist Alfred Eugene Megerlin. In 1959, Johnny, his older brother Robert L. Crawford, Jr., a co-star of NBC's Laramie series, and their father Robert, Sr., were all nominated for Emmy Awards (the brothers for acting and their father for film editing).
Disney started out with 24 original Mouseketeers. But, at the end of the first season the studio reduced the number to 12 and Johnny was released from his contract. His first important break as an actor followed with the title role in a Lux Video Theatre production of, "Little Boy Lost," a live NBC broadcast on March 15, 1956. He also appeared in the popular western series The Lone Ranger in 1956 in one of the few color episodes of that series. Following that performance, the young actor worked steadily with many seasoned actors and directors. By the spring of 1958, he had also performed 14 demanding roles in live teleplays for NBC's Matinee Theatre, appeared on CBS's sitcom, Mr. Adams and Eve, in the Wagon Train episode "The Sally Potter Story" (in which Martin Milner also appeared) and on the syndicated series, Crossroads, Sheriff of Cochise and Whirlybirds and made three pilots in the hope of being on a TV series. The third pilot, which was made as an episode of Dick Powell's Zane Grey Theater, was picked up by ABC and the first season of The Rifleman began filming in July 1958.
Crawford was nominated for an Emmy Award at age 13 for his role as Mark McCain, the son of Lucas McCain, played by Chuck Connors, in the Four Star Television series The Rifleman, which originally aired from 1958 to 1963. Throughout The Rifleman's five seasons, there was a remarkable on-screen chemistry between Connors and Crawford in the depiction of their father-son relationship. They were still close friends when Connors died on November 10, 1992, and Crawford gave a eulogy at Connors' memorial.
During the late 1950s and early 1960s, Crawford had wide popularity with American teenagers and a recording career that generated five Billboard Top 40 hits, including the single, "Cindy's Birthday," which peaked at #8, in 1962. His other hits included "Rumors" (#12, 1962), "Your Nose is Gonna Grow" (#14, 1962) and "Proud" (#29, 1963).
Late in 1961, Crawford appeared as Victor in the episode "A Very Bright Boy" of the ABC sitcom, The Donna Reed Show. Earlier, his brother Robert had also been a guest star on The Donna Reed Show.
While enlisted in the United States Army for two years, Crawford worked on training films as a production coordinator, assistant director, script supervisor and occasional actor. His rank was sergeant at the time of his honorable discharge in December 1967.
In 1968, Crawford played a soldier wanted for murder in, "By the Numbers," an episode of the popular TV series Hawaii Five-O, starring Jack Lord.
Since 1992, Johnny Crawford has led a California-based vintage dance orchestra which performs at special events. His band has been sponsored by the Playboy Jazz Festival; and the orchestra has been the repeated choice for fifteen annual Art Directors Guild Awards shows at the Beverly Hilton, in Beverly Hills, CA. A remastered version of the orchestra's highly rated first album, "Sweepin' the Clouds Away," was officially released on September 30, 2011.
In 2012, Crawford did an introductory commercial for The Rifleman for MeTV, saying, "Watch me on 'me,' MeTV, on The Rifleman!"