Iarlaithe was a member of the Dál Fiatach, a ruling dynasty centered on Downpatrick in east Ulster who were named after Fíatach Finn, a High King of Ireland who reigned in the 1st century A.D. Several of Iarlaithe's close family were saints.
This genealogy is also confirmed in the Naemsenchus Náemh nÉrenn as- .