Ailill was said to be the son of Nath Í and Ethne ingen Chonrach Cais.
The broad agreement of generally pro-Uí Néill sources that Ailill was High King is offered as proof that this was the case.
Ailill is said to have become High King following the supernatural death of Lóegaire mac Néill, supposedly c. 463.
Tradition has him killed in battle at Faughan Hill, fighting against the sons of Niall.
Opposing the view that Ailill was included as a High King from the earliest times, Thomas Charles-Edwards suggests that the inclusion of Nath Í and Ailill Molt was a means to reinforce links between the Uí Néill and the other branches of the Connachta in the late 7th or 8th centuries, when he presumes the king lists and the annals related to Saint Patrick to have been collected and edited.