[3] Before acquiring the rulership of Uisnech, the annals record Oengus' involvement in the feud between the rival midland dynasties of Clann Cholmáin and Síl nÁedo Sláine.
In 612 he won the Battle of Odba (near Navan, Co.Meath) in which Conall Laeg Breg mac Áedo Sláine was slain.
[4] This battle may have been caused by Conall's claims to succeed Áed Uaridnach as high king who died in 612.
[6] According to entries in the Irish annals reporting Óengus's death in 621, which incorrectly call him a son of Colmán Már, he was regis Nepotum Neill or ríg h-Úa Neill, that is king of the Uí Néill.
It is suggested that the explanation for this is that when Suibne Menn killed Máel Coba mac Áedo in 615, he supported Óengus's claims rather than taking power himself, or perhaps that Óengus was a deputy king in the south.