First Prize in viola, counterpoint and harmony, he was a violist at the Orchestre de la Société des Concerts du Conservatoire.
Vincent d'Indy encouraged him to direct the orchestra, and in 1924, Siohan conducted the premiere in Paris of Le Roi David by Arthur Honegger.
In 1929 he founded the "Concerts Siohan", which he conducted until 1936 and where he premiered many French contemporary works, including L'ascension by Olivier Messiaen in 1934.
Siohan defended a doctoral thesis at the Sorbonne (Théories nouvelles de l'harmonie) which was published two year later.
He worked for more than half a century in the family home of his wife Corrie Renan-Psichari-Siohan, the Scheffer - Renan Hotel, in the Nouvelle Athenes district, which became the Musée de la Vie Romantique in 1987.