Ruick achieved success in radio prior to signing as a contract player with Metro-Goldwyn-Mayer. She was heard in the original radio version of Dragnet. She also recorded several songs for MGM Records. In the 1950s, Ruick starred as Kay in the first LP recording of the songs from George Gershwin and Ira Gershwin's 1926 Broadway musical, Oh, Kay!. This was a studio cast recording released by Columbia Records, and conducted by Lehman Engel. Despite what is sometimes claimed, it did not use the original orchestrations, but was the most complete recording of the score made up to that time. She landed a job on Hollywood Screen Test, a talent show which aired on ABC Television from 1948-1953. Ruick appeared on the Kraft Television Theater, soap operas, and The College Bowl (1950), which was hosted by Chico Marx. She also performed for fifteen weeks on the Jerry Colonna Show. In 1955 she was a regular on The Johnny Carson Show.
Ruick married actor Robert Horton Jr., in Las Vegas, Nevada, on August 22, 1953. She had co-starred with Horton in the movie Apache War Smoke the previous year. The couple separated just prior to their second wedding anniversary in 1955 and divorced in 1956, just after he accompanied her to the world premiere of Carousel. She was the wife of Composer John Towner Williams, who composed the music for Star Wars, amongst others, from 1956 until her death. Following her marriage to Williams, Ruick appeared in few motion pictures. They had three children together.
She made guest appearances on The Millionaire (1957), Public Defender (1954), Brothers Brannigan (1960), The 20th Century Fox Hour (1956), and Climax Mystery Theater (1955). She had bit parts in her first four films, one of them being The Band Wagon (1953), and then graduated to supporting roles. Her best remembered roles both came from Rodgers and Hammerstein. She played Carrie Pipperidge in the film version of Carousel (1956) and Esmerelda, one of the wicked stepsisters, in the 1965 TV version of Rodgers and Hammerstein's Cinderella.
Barbara Ruick Williams died on March 3, 1974, aged 43, from a cerebral hemorrhage in Reno, Nevada while on location with her last film, Robert Altman's California Split, which is dedicated to her. She had a cameo role as a barmaid. She was interred at Forest Lawn Memorial Park, Glendale, California.