Christoff was born in Plovdiv, Bulgaria. He sang in the Gusla Choir. King Boris of Bulgaria gave him a private stipend to study in Rome. He studied with Riccardo Stracciari. He also studied in Salzburg, Austria. After World War II, Christoff lived in Rome. In 1950, he was hired to sing the title role in "Boris Godunov" at Covent Garden. This became the role he was known for. He sang in the United States. He never sang at the Metropolitan Opera. Problems with his visa made this impossible.