Zadek, the oldest of three daughters of Elizabeth (Freundlich) and Alex Zadek, was born in Bromberg, Province of Posen, on 15 December 1917.[3] After her hometown became Polish after World War I, her parents moved to Stettin in 1920,[4] where Zadek spent her youth.
However, as a Jew she was forced to leave Germany in 1934 and settled in then Palestine, where she worked as a nurse and shoe saleswoman in Jerusalem, while studying voice with Rose Pauly. In 1945, she returned to Europe and studied at the Zurich Conservatory with Ria Ginster.[5]
Zadek made her debut at the Metropolitan Opera in New York as Donna Anna in Don Giovanni on 26 November 1952. Beside Donna Anna (4 performances), at the Met she sang Eva in Die Meistersinger von Nürnberg (2 performances), Elsa in Lohengrin (1 performance), and the title role of Aida (1 performance on 14 January 1953, her last at the Met). She also appeared at the San Francisco Opera and the Teatro Colón in Buenos Aires. Beginning in 1967, she taught at the Vienna Music Academy, and gave masterclasses. Her last performance at the Vienna State Opera was as Gerhilde in Die Walküre on 3 January 1971, and the same year she retired from the stage.[8]
Zadek died in Karlsruhe on 21 February 2019 at the age of 101.[10]
For the promotion of young musicians, the Hildegard Zadek Foundation has held the biennial International Hilde Zadek Voice Competition since 2003.[11] Through her father, Zadek was a cousin of noted art collector Heinz Berggruen.[12]