Later that year Alexander was invited to establish a music theatre in Norway, and the family moved to Kristiania. Alexander retired from singing and concentrated on building the Opéra Comique, doing everything from hiring the artists to making the costumes. One member of the company was a young soprano named Kirsten Flagstad, who became a family friend and later a supporter and colleague as Varnay's career progressed. When the Opéra closed in 1921 due to financial problems, the Varnays sailed for Buenos Aires, where Mária sang and Alexander directed. They then sailed to New York in November 1923 for what was thought would be a stopover on the journey back to Europe, however Alexander fell ill and died in June 1923.

Varnay auditioned for the Met in June 1940, the following November, and again in May 1941, when she was offered a three-year contract. Her scheduled debut was to be as Elsa in Lohengrin in early 1942, however she started a little earlier than planned. On December 6, 1941 Varnay had to substitute for an ill Lotte Lehmann in the role of Sieglinde in Die Walküre. Her success was heard all around the United States, as it was a Saturday afternoon matinee broadcast. Six days later she replaced Helen Traubel as Brünnhilde in the same opera – a debut that has never been equalled at the Met. It also foreshadowed the “switch-hitter” role she was to play in coming years, as a regular substitute for Traubel at the Met and Martha Mödl at Bayreuth.

In the new year Varnay sang her scheduled roles of Elsa, Elisabeth (Tannhäuser) and Telea in the world premiere of Menotti's The Island God. Later she sang Venus (Tannhäuser), Isolde, Ortrud (Lohengrin), and Eva in Die Meistersinger von Nürnberg. In the mid '40s she suffered vocal problems, stemming from a still-growing body tackling heavy repertoire (she was in her mid 20s); however she worked through these with Paul Althouse, a tenor who retired from the Met in 1941.

At the Met Varnay primarily sang Wagner, and had to go elsewhere to expand her repertoire. She took on Strauss: Salome in Cincinnatti in 1948, Elektra under Mitropoulos in 1949. She also sang Italian roles outside the Met: Aida, Leonora (Il Trovatore), and Gioconda. Apart from singing "Pace, pace mio Dio" (La forza del destino) and "Ritorna vincitor" (Aida) twice each at concerts, she sang no Italian repertoire at the Met until Simon Boccanegra in the 1949/50 season. Then she was given Santuzza (Cavalleria Rusticana), and sang Lady Macbeth in Florence and later Germany. As well as Brünnhilde, she sang Aida and Leonora at Covent Garden in 1951. It would have been interesting to hear her develop in more of these roles.

But the greatest chapter of her career now opened. In 1951 the Bayreuth Festival was due to reopen for the first time after the war. Initially Wieland Wagner had approached Kirsten Flagstad to appear, but she declined, suggesting Varnay instead. After recommendations from a total of twenty-seven people the Wagners invited Varnay to sing at the Festival without an audition. That year she sang Brünnhilde in the Ring under the baton of Herbert von Karajan. For most of the 1950s Varnay was the major soprano artist at Bayreuth, appearing as Brünnhilde, Isolde, Ortrud, Kundry (Parsifal), and Senta (Der fliegende Holländer). As a singing actress she had few peers: when reproached for the apparent blandness of his stage settings, Wieland Wagner riposted with, "Why do I need a tree when I have Astrid Varnay?"

Meanwhile Rudolf Bing had become Manager of the Met, and Wagner and his singers did not fare well under Bing’s reign. Varnay knew she was not appreciated when she was all but ignored after she rescued a performance of Götterdämmerung after a marathon flight across the country, with her husband seriously ill in Texas. Bing's bizarre casting decisions did not help: in 1954 he had the world's then-greatest Brünnhilde and Wotan, Astrid Varnay and Hans Hotter, singing Sieglinde and Hunding in Die Walküre. After Weigert's death in 1955 Varnay decided to leave the Met and base herself in Europe. Settling in Munich, she became a regular guest artist in several houses, principally the Bayerischer Staatsoper in Munich and Deutsche Oper am Rhein (Düsseldorf and Duisberg). She also sang in Salzburg, Vienna, Berlin, Barcelona and Paris, among many other places.

Having made her final Bayreuth appearance in 1967, Varnay sang her last Elektra and Siegfried Brünnhilde in 1969, her last Santuzza and Walküre Brünnhilde in 1970, and her final Götterdämmerung Brünnhilde in 1971. But she added the Kostelnicka (Jenufa) and the Mother in Hänsel und Gretel to her repertoire in 1968, Klytämnestra (Elektra) in 1972, Kabanicha (Kata Kabanova) in 1974 and Mamma Lucia (Cavalleria Rusticana, 1977, which she recorded with Riccardo Muti). She also had success as Claire Zachanassian in Gottfried von Einem's Der Besuch des alten Dame (1972). In these roles Varnay never tried to make herself sound like a mezzo, but sang in the same soprano voice she already used, without any attempt to darken the colouring.

Varnay returned to the Met in late 1974 as the Kostelnicka and sang in several seasons until her final Met appearance on December 22, 1979 as Leokadja Begbick in The Rise and Fall of the City of Mahagonny. Her Herodias and Klytämnestra were filmed by Götz Friedrich (Salome in 1974 and Elektra in 1981), the latter being the last time she sang under the baton of Karl Böhm.

Gradually the major roles were retired and Varnay performed in character role such as Filippyevna in Eugene Onegin, the Countess de Coigny in Andrea Chenier (which she recorded for Decca under Riccardo Chailly), Komorna in Vec Makropoulos, the Countess in Pique Dame, and the Nurse in Boris Godunov, in which she made her final stage appearance in Munich in 1995.

Varnay’s autobiography, written with Donald Arthur, appeared in German as Hab mir's gelobt (Berlin: Henschel Verlag, 1997) and in English as Fifty-five Years in Five Acts (Lebanon, NH: Northeastern University Press/University Press of New England, 2000). With the advent of the compact disc (and internet retail) her recordings are more widely available than ever. Testament issued the 1951 Bayreuth Götterdämmerung in 1999, and will issue the 1955 Bayreuth Ring in 2006. Deutsche Grammophon released a 3-disc retrospective in 2003, and many live performances and radio broadcasts are available on boutique labels. Her reputation is assured for future generations.

Astrid Varnay passed away in Munich on September 4, 2006.

Bayerischer Kammersängerin (1963)

Member of the Bayerischen Maximiliansordens für Wissenschaft und Kunst (1981)

Wilhelm-Pitz-Preis (1988) (awarded by die Vereinigung deutscher Opernchöre und Bühnentänzer in der Deutschen Angestellten-Gewerkschaft on the recommendation of the Bayreuth Festival Chorus)

Meistersinger-Medaille for services to the Bayerische Staatsoper (2003)