In his time there was a rivalry between the northern septs of the Síl nÁedo Sláine, including the Uí Chonaing sept of Cnogba and the Síl nDlúthaig of Fir Cúl, with the southern sept of the Uí Chernaig. Conall's brother Niall mac Cernaig Sotal had been killed by the Uí Chonaing king ofBrega, Írgalach mac Conaing Cuirre The kingship of Brega at this time was in rivalry between the septs. Two contemporaries were also considered kings of Brega around this time, Amalgaid mac Congalaig of the Uí Chonaing, and Conall Grant's nephew, Fogartach mac Néill. Conall is among the guarantors of the Cáin Adomnáin proclaimed at the Synod of Birr in 697 where he is given the title King of Deiscirt Breg or southern Brega. 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 In 712, his nephew Maine mac Néill was slain in battle versus Flann mac Áedo of the Síl nDlúthaig. In 714, his nephew Fogartach was deposed from the kingship and went to Britain possibly by the high king Fergal mac Máele Dúin of the Cenél nEógain. Conall may have acquired the rule of Brega and in 715 he was responsible for the assassination of Murchad Midi, the King of Uisnech from the Clann Cholmáin, possibly the deputy of Fergal. His nephew Fogartach returned to the rule of Brega in 716. Then, in 718 Conall fought the Battle of Cenannas and defeated and slew Amalgaid of Cnogba and his brother Fergal, along with their allies, Gormgal mac Áedo of Síl nDlúthaig and Tuathal Ua Fáelchon of Clann Cholmáin Bicc. The high king Fergal intervened and had Conall killed two months later. The descendants of Conall known as the Síl Conaill Graint based at Calatruim developed a rivalry with the descendants of his brother Niall, the main Uí Chernaig line at Lagore, within the southern Brega septs of Síl nÁedo Sláine. Conall's son Niall mac Conaill Graint was a King of Southern Brega. Another son, Ailill mac Conaill Graint was slain at the Battle of Allen where the men of Leinster defeated the Ui Neill.