Kirchschlager was born in Salzburg, Austria, in 1966. She initially studied piano, her first advanced training on it coming at the Salzburg Mozarteum. In 1984 she enrolled at the Vienna Music Academy, where she studied voice with renowned baritone Walter Berry and with Gerhard Kahry. Oddly, she also studied percussion there for a time.
Kirchschlager soon launched her career with appearances at the Graz Opera House and Wiener Kammeroper. In 1991 she took third prize in the Hans Gabor Belvedere Singing Competition held in Vienna. She joined the Vienna State Opera in 1993, where she successfully debuted in the role of Cherubino. She soon began to draw international notice.
Her first major recordings appeared in 1997 when Sony released a disc of lieder by Mahler, Korngold, and Alma Mahler, with Helmut Deutsch on piano. In the early years of the new century, Kirchschlager appeared on a spate of major recordings that included two discs of Bach arias on Sony (2002), Le nozze di Figaro on Harmonia Mundi (2004), and a DVD entitled Sounds like Christmas containing works by J.S. Bach, Handel, and other composers on EuroArts (2004). Kirchschlager's busy schedule for 2007 included appearances in Vienna in January singing Idamante from Mozart's Idomeneo and in London in May singing Mélisande. In 2011, she performed the title role in Britten's The Rape of Lucretia at the 64th Aldeburgh Festival, as well as at the Theater an der Wien.
She has won three Echo Klassik awards and a Grammy Award for her recording of Le Nozze di Figaro with René Jacobs.