Sidonius was an Irish-born French monk and saint. He was the spiritual teacher of Leutfridus.
Sidonus was born sometime in the seventh century, and was a monk at the abbey in Jumieges in 664; he then spent several years travelling between monasteries. For ten years he served in Rome as a companion to Ouen, eventually being sent to found a monastery near Rouen. This monastery, known as Saint-Saëns, survived until the ninth century. Sidonius founded several other monasteries in the area before retiring to live as a monk.
Sidonius died around 690; his feast day is November 14.