His voice was notable for its range, a true infra-bass (or oktavist bass, lower than basso profondo), including full, resonant low and very-low notes with relaxed vibrato; also for its unusual combination of extreme size and a purring, contrabassoon-like timbre. Although it was a large enough sound for most of Wagner's noble-bass roles, he was not a thunderer and he never performed as Hagen, Hans Sachs, nor Wotan. His interpretations tended to be restrained and intelligent, even in buffo roles like Baron Ochs and Osmin.
Moll was born in Buir, near Cologne, Germany. As a child, he played the cello and hoped to become a great cellist. He also sang in the school choir, the conductor of which encouraged him to concentrate on singing. He studied voice at the Köln Hochschule für Musik with Emmy Müller. He joined the Cologne Opera at 20 and remained until 1961. He then sang for three years in Mainz and five years in Wuppertal. In 1969, he accepted an engagement with the Hamburg State Opera, and he then sang in all the major opera houses of Europe.
He made his US debut with the San Francisco Opera as Gurnemanz in Richard Wagner's Parsifal in 1974, a role he reprised with that company in 2000. His Metropolitan Opera debut followed four years later, when he sang the Landgraf in Tannhäuser, Rocco in Fidelio and Sparafucile in Rigoletto. From that time he performed all over the world.
He made a great many recordings of opera, sacred music, and lieder with many of the great conductors and piano-accompanists, winning several prestigious European record awards; he also won a 1990 Grammy Award for his participation in James Levine's 1988 recording of Das Rheingold. Moll can be heard as Ochs in no fewer than seven complete recordings of Der Rosenkavalier, as Sarastro in six recordings of Die Zauberflöte, as Marke in six sets of Tristan und Isolde, and as the Archangel Raphael in three recordings of Haydn's Die Schöpfung. His recording for the Orfeo label of Schubert's philosophical "Lieder für Bass" set a new standard for these songs. On commercial video as well he can be seen in many roles, including Sarastro (twice), Osmin, the Commendatore, Bartolo (Mozart), Hunding (three times), Gurnemanz, and Ochs (three times).
Kurt Moll retired from the stage in 2006, after singing the Commendatore in Don Giovanni and, his last role, the Nachtwächter in Die Meistersinger von Nürnberg, both for the Bavarian State Opera in Munich. He gave a master class in January 2011 at Carnegie Hall.
He lives in Cologne with his family.