Domhnall ua Néill (old spelling: Domnall ua Néill) was High King of Ireland from 956 to 980.
Domnall was the son of Muirchertach mac Néill, and grandson of Niall Glúndub, a member of the Cenél nEógain northern Uí Néill. He became co-King of Ailech with his brother Flaithbertach on the death of his father in 943. He became High King of Ireland on the death of his maternal cousin Congalach Cnogba of the southern Uí Néill sept of the Síl nÁedo Sláine.
Domnall is considered to have been an effective ruler who introduced military reforms later credited to Brian Boru. Much of his reign was spent in war against his sister Dúnflaith's husband Amlaíb Cuarán, the King of Dublin. In 980 he abdicated and entered the monastery Armagh where he died shortly afterwards.
Domnall was called "High King of Ireland" (ard-rí Érenn) in his obituary, and was the last of his family to hold the title. He was succeeded by Máel Sechnaill mac Domnaill of Clann Cholmáin.