Amalgaid mac Congalaig (died 718) 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 Cuirre (died 696). He ruled in north Brega from 702 to 718. The feud among the southern and northern septs had been intensified by the murder of Niall mac Cernaig Sotal (died 701) by Amalgaid's uncle Irgalach mac Conaing Cuirre (died 702).This was intensified when Amalgaid's ally Flann mac Áedo (died 714) of Síl nDlúthaig defeated and slew Maine mac Néill of Uí Chernaig in battle in 712.