Fahey was born at Killomoran, Gort, and educated in the town's national school and St. Jarlath's, Tuam.
In 1876 he was appointed parish priest at Peterswell, County Galway and remained there till his death in 1919.
He worked with Lady Gregory in promoting the Irish language.
He was elected to the Royal Irish Academy in 1910 and was a founder member of the Galway Archaeological and Historical Society.
He died on 15 March 1919 and is buried in the cemetery of St. Colman's Church, Gort.