In 1939, he gave the first performance of Francis Poulenc's Organ Concerto. In 1943 he became professor of harmony at the Conservatoire de Paris, where he worked until 1970. In 1947, Duruflé wrote his famous "Requiem" op. 9, for soloists, choir, organ and orchestra. In the same year Marie-Madeleine Chevalier became his assistant organist at St-Étienne-du-Mont. They married in 1953 after Duruflé divorced his first wife. The couple often travelled together to give organ recitals together. They always spent many hours practising on the organs on which they had to perform, often practising a lot of the time without the sound so that their fingers were really used to the feel of the organ.