A native of Cleveland, Ohio, McBain moved to the Hollywood area at an early age and began her show business career as an adolescent model in print and television advertisements. During her senior year at Glendale High School, while appearing in a Los Angeles play, she was spotted by a Warner Bros talent scout and added to the studio's roster of contract performers who were appearing in an assembly line-style mass production of TV episodes and theatrical features.
Starting with the September 13, 1955, premiere of the hour-long, three-shows-in-one Warner Brothers Presents, the studio's TV arm, Warner Brothers Television, provided ABC with nearly 20 shows, including seven Western and four detective series. At the age of 17, she was immediately put to work, making her TV acting debut in two episodes of Maverick, March 8 with Jack Kelly and November 22, 1959, with James Garner, as well as the October 16 episode of 77 Sunset Strip. Her first director, at the helm of the March 8 installment, "Passage to Fort Doom", was veteran actor Paul Henreid.
Having received a positive reaction to McBain's initial performances, the studio realized it had a potential star under contract. She was given a prominent ingenue role in her first feature, Ice Palace. The filmed-on-location Technicolor epic was released on January 2, 1960, to mixed reviews, but McBain's notices were generally favorable.
Warner Bros continued to keep McBain busy during 1960 with numerous appearances on their TV shows. She returned to 77 Sunset Strip on February 26, then nine days later found herself back in the 49th state milieu with a guest role in the March 6 installment of The Alaskans.
Eight days later, she was in Bourbon Street Beat and the following day on Sugarfoot. Another episode of Bourbon Street Beat followed two weeks later, on March 28, and still another 77 Sunset Strip on May 6. In eight more days, she was in an episode of Lawman, and three weeks thereafter, on June 6, a third episode of Bourbon Street Beat in as many months.
McBain had a banner year in 1960. In addition to appearing in a top feature film and guest-starring in eight TV episodes, she was assigned two more theatrical features. The first offered her one of three ingenue roles in a major "A" film, Parrish, and the other was a title role in her own "B"-film vehicle, Claudelle Inglish when she replaced the original choice for the lead, Anne Francis. She was given what would turn to be her only regular part in a prime-time series, Daphne Dutton on Surfside 6. When 77 Sunset Strip kicked off its sixth and final season in 1963 with a special five-part story called 'Five', McBain played opposite Efrem Zimbalist, Jr. as "Carla Stevens".
McBain also appeared in many other 1960s TV shows, such as Maverick, Burke's Law, Batman, and The Man from U.N.C.L.E., as well as such films as The Caretakers (1963), Mary, Mary (1963), A Distant Trumpet (1964) and The Karate Killers (1967; a feature film combining two of her UNCLE episodes). She toured Vietnam in 1966 as part of Bob Hope's USO shows.
McBain later developed an image as a villainess, particularly in movies such as I Sailed to Tahiti with an All Girl Crew (1968), Maryjane (1968) and The Mini-Skirt Mob (1968). The last movie had her killed off as an especially vicious biker. She is remembered for her roles in Spinout (1966), Thunder Alley (1967), and The Sidehackers (1969).
During the 1970s, McBain slowed her career somewhat to care for her son Evan, though she continued to make guest appearances in a number of television series. She was featured in the horror film Wicked, Wicked (1973), in yet another bad girl role. She remained active through the 1990s and into the new millennium, playing such character roles as a grandmother on Sabrina, the Teenage Witch, and appearing in such films as Puppet Master 5: The Final Chapter (1994) and The Broken Hearts Club: A Romantic Comedy (2000).
In 1982, McBain was accosted and raped by two men in West Hollywood, and began a second career as a rape victim counselor.