Born Maria Theresa Fischer, she studied in Berlin with the great soprano Lilli Lehmann, and later in Stuttgart and Prague. She made her debut in 1927 at the Basel Stadttheatre, and remained there until 1935. She then sang in Frankfurt (1935-41), and joined the Stuttgart Opera in 1941.
After the war, she began appearing at the Munich State Opera, the Vienna State Opera, at La Scala in Milan, at La Monnaie in Brussels, the Royal Opera House in London, the San Carlo in Naples, and in 1951 at the Teatro Colon in Buenos Aires.
Her repertory included; Gluck's Orfeo, Azucena, Amneris, Eboli, Ortrud, Fricka, Brangane, Die Amme, Herodias, Clytemnestra, The old Countess, Kostelnicka, Jocasta, The Gingerbread Witch, etc. She created the title role in Carl Orff's Antigonae at the Salzburg Festival in 1949.
Fischer enjoyed a long and distinguished career, singing until 1965.