Uí Fiachrach Muaidhe were a branch of the Ui Fiachrach dynasty of the Connachta. They were centered in the Moy River valley of Co. Mayo. Their territory, Tír Fhíachrach Múaidhe, (now in Co. Sligo) at its widest reach included the territories of Irrus Domnann and Tír Amhalgaidh now in Co. Mayo. This branch of the Ui Fiachrach was descended from Fiachnae, a brother of Ailill Molt (died 484), high king of Ireland. Later their chief sept was the Ó Dubhda (O'Dowd), princes at Carn Amalgaidh, near Killala, Co. Mayo.
They provided some Kings of Connacht, including: