Muirchertach Ceannfada O'Neill (Irish: Muirchertach Ceannfada Ó Néill), also known as Murtagh O'Neill and Maurice O'Neill, was a lord of Clandeboye in medieval Ireland. He succeeded his father, Henry O'Neill, to the kingship of Clandeboye after his death in 1347. In 1354 his forces along with the English inflicted a heavy defeat on , king of Tyrone.