Kirchschlager began her musical training at the Mozarteum in Salzburg, where she studied percussion and piano. In 1984, she went to the Vienna Music Academy, where she studied with Gerhard Kahry and Walter Berry. Her first engagements were at the Wiener Kammeroper and the Graz Opera House. Kirchschlager won third prize in the International Hans Gabor Belvedere Singing Competition in 1991. Her stage debut was in Graz in 1993 as Octavian (Der Rosenkavalier). In 1993, she became a member of the Vienna State Opera, and made her debut there as Cherubino (The Marriage of Figaro). Also in 1993, she was awarded the Mozart Medal of the Mozartgemeinde Wien.
In 2002, Kirchschlager sang the role of Sophie in the world première of Nicholas Maw’s opera Sophie’s Choice at the Royal Opera House in London, the American premiere of the revised version of the opera at the Washington Opera, and the Austrian premiere at Volksoper Wien. She is a regular guest of the annual Lieder festival Schubertiade Schwarzenberg in Vorarlberg, Austria. Her regular collaborators include Helmut Deutsch and Simon Keenlyside.
Kirchschlager resides in Vienna. She has a son, Felix, from her marriage to the baritone Hans Peter Kammerer. Kirchschlager and Kammerer are currently separated.