He appeared regularly at the Staatsoper for the next 35 years, in a total of 1,480 performances, and the company awarded him honorary membership in 1982.
Beginning in 1956, he appeared outside Austria, in places such as Milan, Rome, Paris, Amsterdam, Brussels, Teatro Colón in Buenos Aires, Berlin, and Munich (Idomeneo, Jenůfa, Die Frau ohne Schatten, and Les contes d'Hoffmann (The Tales of Hoffmann).
Kmentt continued to sing into his sixties, in character roles such as Triquet in Eugene Onegin, the Innkeeper in Der Rosenkavalier and Altoum in Turandot, while teaching at the Vienna Music Academy.
His final Vienna State Opera performance was on 25 November 2005 as the Haushofmeister in Ariadne auf Naxos.
He also recorded Narraboth under Rudolf Moralt in 1952 for Philips (Columbia in the U.S.) and sang the role in Vienna in 1972 under Karl Böhm in a live performance that later appeared on RCA and some "pirate" labels.