Born in Salinas, California, she grew up in Durant, Oklahoma as an only child on her father's cattle ranch. In her words, Gail recalled that she learned music from her mother who taught her piano lessons while her father taught her to ride horses. She began to perform publicly at age six in church, rodeos, talent shows and on pickup beds on the back of trucks stumping for local political candidates. She also learned how to sing gospel music from her grandmother.
While attending the University of Tulsa, majoring in piano performance, she took part in the Miss Oklahoma Pageant and won in talent and swimsuit competitions. She also attended the Juilliard School of Music in New York during the summer to further hone her talents as a piano player. After graduating Magna Cum Laude in 1969, she flew out to Los Angeles originally to study the Yamaha Method for teaching pre-school children music, but decided to audition for Lawrence Welk while he and his band performed every Saturday night at the Hollywood Palladium. She got the maestro's attention in a tag dance, tapping him on the shoulder and asking if she can sing for him. In a matter of minutes, she did, singing Cotton Fields in front of three thousand people at the Palladium which Welk liked, and asked her to appear on the opening broadcast the following September.
Gail officially joined the Musical Family three shows into the 1969-70 season and over the course of the next twelve years, she sang solos, played piano, sang in duets with Dick Dale and in trios; first with Sandi Griffiths, and Mary Lou Metzger and later for "Gail, Ron & Michael" a mixed trio that featured her husband Ron Anderson and Michael Redman. In addition, she also developed as a songwriter, writing vocal arrangements for both trio groups. Her exposure on The Lawrence Welk Show opened doors in her career, making notable television appearances on Match Game, Dinah!, and The Mike Douglas Show. The lieutenant governor of Oklahoma even christened "Gail Farrell Drive" in her honor in Durant.
Since regular production on the Welk show ceased in 1982, Farrell continued to pursue singing/songwriting, as her arrangements have been covered by artists such as Barbara Mandrell and featured on the soap opera Knots Landing. She also has sung with numerous recording artists and her vocals have appeared in numerous commercials and television/film soundtracks.
She still sings in her own right, either as a solo artist or with her fellow Welk stars. In recent years, she has appeared on several Welk-related television specials for PBS such as Milestones & Memories and Lawrence Welk, Precious Memories. Farrell also joined forces with fellow Welk castmates Ava Barber, Ralna English and Mary Lou Metzger for the four-woman revue, Four Wunnerful Women.
Farrell married Ron Anderson on December 7, 1979. They make their home in Northern California and are the parents of twin daughters, Erin and Lauren.