Amalgaid mac Congalaig (died 718) was a King of Brega from the UàChonaing sept of Cnogba (Knowth) of the SÃÂl nÃÂedo 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.
Amalgaid's reign was dominated by the feuds among the septs of the SÃÂl nÃÂedo Sláine and the beginnings of the return to power of the Clann Cholmáin of Uisnech. The kingship of Brega at this time was in rivalry between the septs of UàChonaing and the southern sept of the UàChernaig sept of Lagore in south Brega. Two contemporary members of the rival sept, Fogartach mac Néill (died 724) and Conall Grant mac Cernaig Sotal (died 718) were also counted as kings of Brega during this time. The UàChonaing were allied with the SÃÂl nDlúthaig of Fir Cúl Breg.
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 ÃÂedo (died 714) of SÃÂl nDlúthaig defeated and slew Maine mac Néill of UàChernaig in battle in 712.
The high king Fergal mac Máele Dúin (died 722) of the Cenél nEógain seems to have favored Clann Cholmáin in Meath and intervened in the affairs of the midlands. In 711, the Battle of Sliab Fúait (in the Fews, Co. Armagh) is recorded where Fergal was victorious and Cú Raàmac ÃÂedo of SÃÂl nDlúthaig was slain along with the king of UàMéith. In 714, Fergal's southern deputy Murchad Midi (died 715) of Uisnech fought the Battle of Bile Tened (Billywood, Co. Meath) where Amalgaid's ally Flann was slain. The battle was not decisive however. The attention of Fergal then went on the UàChernaig.
In 718, the Battle of Cenannas (near Kells) was fought between the rival septs and Conall Grant of the UàChernaig was victorious. Amalgaid and his brother Fergal were slain along with their allies, Gormgal mac ÃÂedo of SÃÂl nDlúthaig and Tuathal Ua Fáelchon of Clann Cholmáin Bicc.
His sons Conaing mac Amalgado (died 742) and Dúngal mac Amalgado (died 759) were also Kings of Brega.