Cernach mac Congalaig was a King of Brega from the Uí Chonaing sept of Cnogba (Knowth) of the Síl nÁedo Sláine branch of the southern Ui Neill. He was the son of Congalach mac Conaing and brother of Flann mac Congalaig, previous kings. He ruled from 812-818.
- Position held
- Kings of Brega
- Died
- 818
