Joan Marie O'Brien was born to David and Rita O'Brien on Valentine's Day 1936, in Cambridge, Massachusetts. The family moved to California when O'Brien was a child, and enrolled O'Brien in dance classes when she was eight years old. She graduated from Chaffey Union High School in Ontario, California.
O'Brien's singing abilities came to the attention of entertainer and Country Music Hall of Fame member Cliffie Stone, who hired her as a regular performer on his television show Hometown Jamboree before her high school graduation. In 1954, she became a regular on The Bob Crosby Show, and stayed until shortly before the show's cancellation in 1958. She co-starred with Cary Grant and Tony Curtis in the 1959 movie Operation Petticoat.
Lawrence Welk hired O'Brien as a one-week replacement for his champagne lady Alice Lon in July 1959. O'Brien had come to Welk's attention years earlier when she was a singer on Bob Crosby's show, but Welk decided not to hire her at that time because she was still a teenager.
Her most frequent acting performances were in television during the 1960s. She made two guest appearances on Perry Mason: in 1960 she played Betty Roberts in "The Case of the Singing Skirt," and in 1965 she played Jill Fenwick in "The Case of the Lover's Gamble." In 1964, O'Brien guest starred in an episode of The Man from UNCLE. Series star Robert Vaughn subsequently cast her as Ophelia in Hamlet at the Pasadena Playhouse.
Actresses Sheree North, Sabrina and Sue Carson joined O'Brien in a tour of Playgirls in 1961, appearing at the Riverside Hotel in Reno, Nevada.
O'Brien played Elvis Presley's girlfriend in the 1963 vehicle It Happened at the World's Fair.
After her acting career ended, O'Brien sang with the Harry James band in 1968.