Gail Gilmore was born in Washington, D.C. and was raised in New Orleans, Louisiana. She studied at Xavier University, New Orleans, and Indiana University, Bloomington, where she received a Master's degree in music.
She started her career as an artist in Residence in different opera houses in Germany (Wiesbaden, Nürnberg, and Frankfurt). In 1983 she made her first appearance at the Teatro La Fenice in Venice, as Kundry in Wagner's Parsifal, and at the Arena di Verona as Amneris in Aïda. She returned to Verona in 1984 as the title role in Bizet's Carmen. In later years, she returned to Verona several times in various productions. Also in 1984, she made her La Scala debut in Milan as Venus in Tannhäuser. In 1986, she made her debuts at the Metropolitan Opera and at Carnegie Hall as Kundry. She returned to the Met in 1987 as Venus and as the Composer in Strauss' Ariadne auf Naxos, and in 1989 in Wagner's Die Walküre. Also in 1989, she made her debut at the Bolshoi Theater in Moscow as Ortrud in Lohengrin. In 1994 she made her debut at the Teatro Colon in Buenos Aires as the Gräfin in Lulu, and at the Prague Opera as Strauss' Salome.
In 1995 she had her debut as Tosca in Strasbourg. In 1996, she debuted in Germany as Turandot, and in May 1997 she had yet another very successful debut as Elektra. In early 1998, she debuted in the title role of Fosca by the Brasilian composer Carlos Gomes with a very successful tournee in major Brasilian cities. As a versatile singer she also sings in many concerts. She is well known for her "Opera Aria" concerts, but her repertoire also includes Strauss' Four Last Songs, Berlioz's La Mort de Cléopatre, and works by American composers Barber, Berstein, Gershwin, etc.