Born in 1972 in Auray (Morbihan), Auguste Le Guennant studied at the Schola Cantorum de Paris, the organ with Alexandre Guilmant and composition with Vincent d'Indy. He held for some time the position of organist at the grand organ of Notre-Dame de Clignancourt, and left Paris in 1905 to become head of the chapel at Notre-Dame-de-Bon-Port in Les Sables-d'Olonne, and from 1908 at the Basilica of Saint-Nicolas in Nantes. He founded the mixed group A Capella in this city, in collaboration with A. Mahot.
The Mutual Edition of the Schola Cantorum published his Adagietto for organ, and an O Salutaris for four mixed voices. Mr. Biton published an accompanying book on Gregorian chant.
In 1925, Le Guennant arrived at the Gregorian Institute of Paris as director and teacher of Gregorian chant, succeeding Dom Joseph Gajard of the Solesmes Abbey.
After the Second World War, he organized many Gregorian sessions, not only in France but also in Fátima, and even Rio de Janeiro. Still teaching at the Gregorian Institute in Paris, this pedagogue and musician considerably boosted the teaching of Gregorian chant, by creating centres of study in several countries. When Maurice Duruflé thought about basing his Requiem on Gregorian chant, he asked Le Guennant for advice, and gratefully acknowledged his understanding. In 1960, Duruflé dedicated a composition to Le Guennant, his Quatre Motets sur des thèmes grégoriens which were also based on chant.
In 1953, Le Guennant was awarded the Honorary Doctorate of the Pontifical Institute of Sacred Music in Rome.