The daughter of Mr. and Mrs. Virgil Gates, Nancy Gates was born in Dallas, Texas, Gates grew up in nearby Denton, and was described as "a child wonder." A 1932 newspaper article about an Easter program at Robert E. Lee School noted, "Nancy Gates, presenting a soft-shoe number, will open the style show." That same year, she had a part in the Denton Kiddie Revue.
In 1935, she appeared in the production "A Kiss for Cinderella," which starred Brenda Marshall and a minstrel show that included Ann Sheridan, both of whom were from Denton. She was in show Business before she finished high school, having her own radio program on WFAA in Dallas for two years while she was a student at Denton High School, from which she graduated. Musically oriented, Gates was featured as a singer in a 1942 concert by the North Texas Teachers College stage band.
Gates entered acting at a young age, receiving a contract with RKO at the age of 15, which required court approval because of her status as a minor. Orson Welles screen-tested her for a role in the 1942 film The Magnificent Ambersons. Although she did not get the role, which went to Anne Baxter, the test paved the way for her Future entry into film. That same year she had her first credited role, in The Great Gildersleeve. In 1943 she went on contract with RKO, her first film with them being Hitler's Children that same year. She began receiving roles in mostly B-movies, many of which were westerns or sci-fi, eventually receiving lead roles as the heroine. In 1948 she starred opposite Eddie Dean in Check Your Guns, and in 1949 she played alongside Jim Bannon, Marin Sais, and Emmett Lynn in an episode of the Red Ryder serial, titled Roll, Thunder, Roll. She would star in several other films over the next ten years, especially in westerns like Comanche Station (1959), and in support roles, most notably in two Frank Sinatra films, Some Came Running and Suddenly.
Gates played in The Orson Welles Show on CBS Radio in 1941–1942 and in the soap opera Masquerade on NBC in 1946–1947. A February 21, 1944, newspaper article noted that Gates would "appear in a series of air programs for the RKO Studios beginning Feb. 28." In 1951, she starred on Screen Director's Playhouse opposite william Holden in Remember the Night and on Lux Radio Theatre in a supporting role in Sunset Boulevard.
Gates made a total of 55 television appearances. She made two appearances on the television series Maverick, three appearances on Perry Mason, three on Wagon Train, six on Lux Video Theater, and two on Alfred Hitchcock Presents. In 1957 she had a memorable role as defendant Martha Bradford in the Perry Mason episode, "The Case of the Crooked Candle;" then in 1964 she was cast in the role of the defendant, Mary Douglas, in "The Case of the Woeful Widower." In 1965 she again played the role of Perry's client, this time as Claire Armstrong, the title character, in "The Case of the Candy Queen."
She was married to Hollywood attorney and Business manager J. william Hayes, whom she met when he was a commercial pilot and she was a Passenger on one of his flights. They had four children, twin daughters Cindy and Cathy, born November 5, 1960, and sons who became Hollywood producers—Jeffrey M. Hayes and Chip Hayes. Hayes died in 1992.
In total Gates starred or co-starred in 34 films and serials. She retired from acting in 1969.