Niall mac Cernaig Sotal (died 701) was a king in southern Brega of the Uí Chernaig sept of Lagore of the Síl nÁedo Sláine.
In 688 Niall defeated Congalach mac Conaing Cuirre (died 696) of Uí Chonaing and his Ciannachta allies at the Battle of Imlech Pich.
[4] Niall is listed as one of the guarantors of the Cáin Adomnáin ("Law of the Innocents") of Saint Adomnán arranged at the Synod of Birr in 697 where he is called King of Mag Breg.
[1] These titles were added to the list of guarantors in 727 and the first use of the title King of South Brega in the Annals of Ulster is not until 751[5] In 701 Niall was assassinated by the Uí Chonaing king of Brega, Írgalach mac Conaing Cuirre (died 702), at Drumain Ua Casan.
According to the Fragmentary Annals of Ireland, Niall was under Adomnán's protection and the saint cursed Írgalach as a result.