She studied in Vienna with Erik Schmedes, and debuted in Linz in 1919 as Elsa in lLohengrin.
She also sang at the Deutsches Theater in Prague 1921-1923 (where she sang the role of Nettchen in the premiere of the revised version of Alexander Zemlinsky"s opera Kleider machen Leute) and at the Staatsoper, Munich in 1923-1924. On 21 January 1925, she made her debut at the Metropolitan Opera in New York as Sieglinde in Die. The next day, Olin Downes wrote in The New York Times: “young Czechoslovakian soprano. was warmly welcomed.
She has a fresh and youthful voice, a little small for the demands of her role, much grace and sincerity as an actress.
Not often is the figure of Sieglinde so human, so tender and so appealing to the beholder." The same year she sang Donna Elvira in Don Giovanni. She sang a total of 196 performances at the Metropolitan Opera between 1925 and 1935.
She sang there in a number of American premieres including Franco Alfano"s Madonna Imperia (8 February 1928), Pizzetti"s Fra Gherardo (29 March 1929), also in the opera Švanda the Bagpiper by the Czechoslovakian-American composer Jaromír Weinberger (11 July 1931), and Simon Boccanegra (29 January 1932). In 1930-1939, she was a regular Wagnerian singer in Bayreuth.
Some of her major roles were Eva in in 1933, plus Sieglinde and Elsa in 1936.
The New York Herald Tribune wrote in 1936 from Bayreuth: "Müller"s voice is fresher and more beautiful than when she was at the Metropolitan". At Salzburg, she appeared as Eurydice (1931), Reiza (1933) and Donna Elvira (1934). She made her Covent Garden debut as Eva in 1934, and sang Sieglinde in the 1937 Ring Cycles.
Her large repertory included the title roles in Die agyptische Helena, Jenufa and Gluck’s Iphigenie en Tauride, Djula in Gotovac"s Ero the Joker, Pamina, Tosca and Marguerite.
Müller possessed a warm, vibrant voice and sang with a rare purity of tone. (Harold Rosenthal) After World World War II she retired to live at Bayreuth, where she died in 1958.