The vocal talents of Birgit Nilsson were first recognized when she began to sing in her church choir. She studied voice with Ragnar Blennow in Bastad and later at the Royal Music Academy Stockholm with Joseph Hislop and Arne Sunnegärdh. She made her opera debut at Stockholm where her first important role was Agatha in Der Freischütz, and in 1947 she sang Lady Macbeth in Verdi's Macbeth there. Her first important international appearance came in 1951 as Elettra in Mozart's Idomeneo at the Glyndebourne Festival. In 1952, she sang Donna Anna in Don Giovanni at Florence. Her first important appearances in Wagner operas came in 1953 at Stockholm where she sang Elisabeth in Tannhäuser and Isolde for the first time. This marked the start of the most important Wagnerian career of the second half of the 20th century. The following year she made her Bayrueth debut as Elsa in Lohengrin and in the same season sang Ortlinde in Die Walküre. She later appeared there as Isolde and as Brunnhilde. It was in Munich during the 1954-1955 season that she first sang Brunnhilde in Wagner's Der Ring des Nibelungen and during the same season she sang her first Salome. In 1957, she sang the complete Ring cycle in London. At the Vienna State Opera she was heard as Elsa, Sieglinde, Elisabeth, Aida, and Sent. In 1957 she sang Leonore in Beethoven's Fidelio and the following season sang her first Turandot. She was also highly regarded for her interpretations of Elektra and the Barak's Wife in Die Frau ohne Schatten. Her other important Italian roles were Tosca, Amelia in Un ballo in maschera and Aida. She sang at all of the major opera centers of the world including Tokyo, Paris, Buenos Aires, Chicago, San Francisco, and Hamburg. Also she sang Turandot in Moscow with the Teatro alla Scala. At the age of 62, a performance of Strauss' Elektra was videotaped at the Metropolitan Opera House and broadcast around the world.
Because of her full schedule of opera performances, Nilsson did not sing in many concerts or recitals although early in her career she did sing the Ninth Symphony of Beethoven on several occasions, including one at Bayreuth. She did give some recitals including tours of Australia and Japan as well the major music centers of Europe and North America. Her recital programs concentrated on the German and Scandinavian songs, including some rarely heard pieces by Stenhammar. She often sang "I Could Have Danced All Night" as an encore.
The voice of Birgit Nilsson was like a laser beam that cut through the orchestra, unlike the voice of Kirsten Flagstad or Jessye Norman which are like a wall of sound. It was a large voice with such brilliance that at times it gave the sensation of being sharp of the intended pitch. She was a congenial colleague except for her long-standing difficulties with Franco Corelli regarding the length of the high Cs in Puccini's Turandot and with Herbert von Karjan. Happily all of her important roles have been preserved on recordings. As long as the operas of Wagner are performed, the voice of Birgit Nilsson will be remembered, and no one has sung Puccini's Turandot with more brilliance or security. Her autobiography, Mina minnesbilder, was published in 1977 at Stockholm.