Dúngal mac Cellaig was a King of Osraige in modern County Kilkenny. He ruled from 770 to 772. He was of the dynasty that ruled over Osraige in the early Christian period known as the Dál Birn and was the son of Cellach mac Fáelchair

Cellach mac Fáelchair

Cellach mac Fáelchair or Cellach Raigni was a King of Osraige in modern County Kilkenny. He was the son of Fáelchar Ua Máele Ódrain , a previous king....

 (died 735), a previous king.

The Osraige plunged into civil war upon the death of Anmchad mac Con Cherca

Anmchad mac Con Cherca

Anmchad mac Con Cherca was king of Osraige, a kingdom largely situated in modern County Kilkenny and forming part of the kingdom and province of Munster in south and south-west Ireland...

 after 761. Tóim Snáma mac Flainn

Tóim Snáma mac Flainn

Tóim Snáma mac Flainn was a King of Osraige in modern County Kilkenny. He ruled from circa 761 to 770. His exact year of accession is unknown, 761 was the last year his predecessor Anmchad mac Con Cherca was named in the annals....

was opposed by the sons of Cellach, presumably Dúngal and in 761 they were defeated by Tóim Snáma and were put to flight.