Cummascach mac Congalaig was a King of Brega from the Uí Chonaing sept of Cnogba (Knowth) of the Síl nÁedo Sláine branch of the southern Uí Néill. He was the son of Congalach mac Conaing and brother of Flann mac Congalaig and Cernach mac Congalaig, previous kings. He ruled from 818 to 839.
- Position held
- Kings of Brega
- Died
- 839
