Domhnall ua Néill (old spelling:Domnall ua Néill; anglicised asDonal O'Neill) (died 980) wasHigh King of Ireland from 956 to 980.

Domnall was the son ofMuirchertach mac Néill, and grandson ofNiall Glúndub, a member of theCenél nEógain northernUí Néill. He became co-King of Ailech with his brother Flaithbertach ua Néill on the death of his father in 943. He became High King of Ireland on the death of his maternal cousinCongalach Cnogba of the southern Uí Néill sept of theSíl nÁedo Sláine.

Domnall is considered to have been an effective ruler who introduced military reforms later credited toBrian Boru.^{[citation needed]} Much of his reign was spent in war against his sister Dúnflaith's husbandAmlaíb Cuarán, theKing of Dublin. In 980 he abdicated and entered the monasteryArmagh 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 byMáel Sechnaill mac Domnaill ofClann Cholmáin.

Domnall's children included Muiredach, whose son Lochlann may have been the ancestor ofDomnall Ua Lochlainn, and Muirchertach, ancestor of theO'Neills ofTír Eógain. His grandsonFlaithbertach Ua Néill was King of Ailech and the leading figure among the Uí Néill, certainly from the death of Máel Sechnaill in 1022, if not earlier.

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