Siepi commenced singing as a member of a madrigal group; and though largely self-taught won a scholarship to the Milan Conservatory, where he studied briefly. When he was eighteen friends encouraged him to enter a singing competition in Florence. He won first prize and an impresario in the audience engaged him to sing Sparafucile / Rigoletto at Schio, near Venice, in 1941. A committed anti-fascist, Siepi fled to Switzerland in 1943 to avoid conscription by the Nazi forces occupying Italy. While interned his voice again attracted attention and he received some singing lessons in Lugano.

With the end of World War II, Siepi was able to resume his operatic career in 1945, enjoying immediate success as Zaccaria / Nabucco at La Fenice, Ve...