Early career
In 1946, Nilsson made her debut at the Royal Swedish Opera in Stockholm with only three days' notice, replacing the ailing Agathe in Carl Maria von Weber's Der Freischütz. Conductor Leo Blech wasn't very kind to her and, as she wrote in her autobiography, she even contemplated suicide after the performance. In 1947 she claimed national attention as Verdi's Lady Macbeth under Fritz Busch. A wealth of parts followed, from Strauss and Verdi to Wagner, Puccini, and Tchaikovsky. In Stockholm, she built up a steady repertoire of roles in the lyric-dramatic field, including Donna Anna, Aida, Lisa, Tosca, Venus, Sieglinde, Senta, and the Marschallin, one of her favorite roles, all sung in Swedish. In 1949 she sang Ariadne auf Naxos with Hjördis Schymberg and Elisabeth Söderström among others.
Nilsson as Lady Macbeth in the opera by Giuseppe Verdi at the Royal Swedish Opera, Stockholm, 1947.
Under Fritz Busch's tutelage, her career took wing. He was instrumental in securing her first important engagement outside Sweden, as Electra in Mozart's Idomeneo at the Glyndebourne Festival in 1951. Her debut at the Vienna State Opera in 1953 was a turning point; she would be a regular performer there for more than 25 years. It was followed by Elsa in Wagner's Lohengrin at the Bayreuth Festival in 1954, then her first Brünnhilde in a complete Ring at the Bavarian State Opera, at the Munich Opera Festival of 1954. Later she returned as Sieglinde, Brünnhilde, and Isolde until 1969.
She took the title role of Turandot, which is brief but requires an unusually big sound, to La Scala in Milan in 1958, and then to the rest of Italy. Nilsson made her American debut as Brünnhilde in Wagner's Die Walküre in 1956 with the San Francisco Opera. She attained international stardom after a performance as Isolde at the Metropolitan Opera in New York City in 1959, which made front-page news. She said that the single biggest event in her life was being asked to perform at the opening of the 180th season at La Scala as Turandot in 1958. She performed at many major opera houses in the world including Vienna, Berlin, the Royal Opera House at Covent Garden, Tokyo, Paris, Buenos Aires, Chicago, and Hamburg.
She sang with the Sydney Symphony Orchestra in the all-Wagner concert that opened the Concert Hall of the Sydney Opera House in 1973.
From the 1960s through to the 1980s
Nilsson was widely known as the leading Wagnerian soprano of her time, the successor to the great Norwegian soprano Kirsten Flagstad, particularly as Brünnhilde. However, she also sang many of the other famous soprano roles, among them Leonore, Aida, Turandot, Tosca, Elektra, and Salome. She had, according to The New York Times, a "voice of impeccable trueness and impregnable stamina".
The conductor Erich Leinsdorf thought that her longevity, like Flagstad's, had something to do with her Scandinavian heritage, remarking that Wagner required "thoughtful, patient and methodical people." Nilsson attributed her long career to no particular lifestyle or regimen. "I do nothing special", she once said. "I don't smoke. I drink a little wine and beer. I was born with the right set of parents."
In sheer power, her high notes were sometimes compared to those of the Broadway belter Ethel Merman. However, Nilsson claims her "explosive" high notes that were her biggest asset on-stage "have not been recorded like they should have been" in the studio. She later lamented: "It always made me a little bit sad when I heard my own recordings. And many people told me that I sang much better in person than I do on the recordings! That didn't flatter me at all, because I know what's going to be left when I am no longer singing".