Educated as a lawyer, he was heard by the Bulgarian King Boris while singing with the famous Gusla Choir and was granted a scholarship to study singing in Rome under Riccardo Stracciari. He then went to Salzburg for further training under Muratti and made his operatic debut in 1946 as Colline in La Bohème in Reggio di Calabria.
In 1947 he sang the part of Pimen in Boris Godunov both in Rome and at La Scala, and first undertook the title role of Boris at Cagliari in 1948. He made his Covent Garden debut in 1949 as Boris and sang there regularly between 1958 and 1974. He was engaged to sing at the Met in 1950 as Philip II in Don Carlo but was denied entry to the country under the McCarran Internal Security Act; he eventually made his US debut as Boris in San Francisco in 1956. He also sang a number of times in Chicago between 1957 and 1963, and though his career extended to most of the major opera houses of the world, he never appeared at the Met.
Christoff’s perfectly controlled Slavic voice was ideally suited to the Russian repertoire and he was seen by many as the legitimate successor to the great Russian bass Feodor Chaliapin because of his magnetic stage presence, powerful acting and meaningful projection of the text. He was also famous for a number of Verdi bass parts, notably Philip II and Fiesco (Simon Boccanegra), and his German roles included Rocco (Fidelio), King Mark (Tristan und Isolde), Hagen (Götterdämmerung) and Gurnemanz (Parsifal). His concert and recorded repertoire also covered a wide range of music, especially by the composers of the Russian Romantic era.
He died in 1993.