Garrett has had an extensive music career. A graduate of the Royal Academy of Music and an alumna of the prestigious National Opera Studio, she won the Decca Prize of the Kathleen Ferrier Award in 1979, thereby launching her career. Her professional debut, in 1979, was as Amor in Orontea at the music festival in Batignano. She subsequently sang, in 1980, Alice in Le comte Ory at the London Coliseum and Dorinda in Orlando at the Wexford Festival, in 1981, also at Wexford, the title role in Zaide, in 1982 Sophie in Werther with Opera North and in 1984 Damigella in L'incoronazione di Poppea at Glyndebourne. From 1984, as principal Soprano at English National Opera, she became well known for her performances in productions of the operas Serse, Le Nozze di Figaro, Così fan tutte and Die Fledermaus.