Born in New York City, Sullivan fell into acting when in college playing semi-pro football. During the later Depression years, Sullivan was told that because of his 6 ft 3 in (1.9 m) stature and rugged good looks he could "make money" simply standing on a Broadway stage. This began a successful career on Broadway, movies and television.
One of Sullivan's most memorable roles was playing a movie director in The Bad and the Beautiful opposite Kirk Douglas. Sullivan starred opposite Bette Davis in the 1951 film Payment on Demand. In 1950, Sullivan appeared in the film A Life of Her Own and replaced Vincent Price in the role of Leslie Charteris' Simon Templar on the NBC Radio show The Saint. Sullivan only lasted two episodes before the show was cancelled.
In the 1953-1954 television season, Sullivan appeared with other celebrities as a musical judge in ABC's Jukebox Jury. Sullivan's first starring television role was a syndicated adaptation of the radio series The Man Called X for Ziv Television in 1956-1957, as secret agent Ken Thurston, the role Herbert Marshall originally portrayed before the microphone. In the 1957-1958 season, Sullivan starred in the adventure/drama television series Harbormaster. He played a commercial ship's captain, David Scott, and Paul Burke played his partner, Jeff Kittridge, in five episodes of the series, which aired first on CBS and then ABC under the revised title Adventure at Scott Island.
Sullivan appeared again with Bette Davis, on stage, in 1960. Davis and her husband Gary Merrill were touring the US in a theatrical staging of selected prose and poetry of Carl Sandburg, but their marriage was failing, and Sullivan substituted for Merrill.
In 1960, Sullivan played frontier sheriff Pat Garrett opposite Clu Gulager as outlaw Billy the Kid in the NBC western television series The Tall Man (although the series ran for seventy-five half-hour episodes, the one in which Garrett kills Billy was never filmed). Sullivan appeared in Sam Peckinpah's Pat Garrett & Billy the Kid (1973) as John Chisum, but his scene was excised from the release print (though later restored to the film). He had a featured role in the 1976 miniseries Rich Man, Poor Man Book II. In additional to The Tall Man, Sullivan also starred in the television series The Road West, which aired on NBC on Monday, alternating with Perry Como), during the 1966-1967 season. Sullivan played the role of family patriarch Ben Pride.
Sullivan guest starred in many series, including The Ford Show, Starring Tennessee Ernie Ford, The DuPont Show with June Allyson, The Reporter, That Girl," The Love Boat,Little House on the Prairie, The Streets of San Francisco, and McMillan & Wife. He starred in many Hallmark Hall of Fame specials including a highly acclaimed production of "The Price" opposite George C. Scott. Sullivan was consistently in demand for the entirety of his career. His acting career spanned romantic leading man roles to villains and finally tocharacter roles. In his later years, Sullivan had roles in the films, Oh, God! with George Burns and Earthquake, where he shared scenes with Ava Gardner.
Sullivan has two stars on the Hollywood Walk of Fame: one at 1500 Vine St. for his work in television, and another at 6160 Hollywood Blvd. for motion pictures.
His daughter Jenny Sullivan wrote the play J for J (Journals for John) after she found a packet of unsent letters (in 1995) written by Barry decades earlier to her older brother, Johnny, who was mentally disabled. The play premiered on October 20, 2001. John Ritter, who in real life had a handicapped brother, played Johnny, Jenny played herself, and actor Jeff Kober portrayed Sullivan.
Sullivan was a Democratic Party activist and a tireless advocate for the mentally disabled. He had three children. Sullivan was married and divorced three times. Marie Brown, a Broadway actress, was mother to both Jenny and John Sullivan. Gita Hall, model and actress, was the mother of Patricia. His third marriage to Desiree Sumara produced no issue.
Sullivan died of respiratory failure on June 6, 1994, in Sherman Oaks, California.
His daughter, Jenny Sullivan, a former actress, is now a theater director. Younger daughter Patricia "Patsy" was twelve years old when signed to a cosmetic company contract as their "face" and was a cover girl featured on many national magazines as well as in commercials. As a teen she married songwriter Jimmy Webb, with whom she had five sons and a daughter. Three of Patsy's sons formed the rock group "The Webb Brothers" and have enjoyed success. Jenny Sullivan married musician Jim Messina; they have no children.