He was the son of Indrechtach mac Lethlobair (died 741), a previous King of Dal nAraide.
They were successful and the incumbent king Cináed Ciarrge mac Cathussaig and his ally, Dúngal king of the Uí Tuirtri (an Airgialla tribe west of Lough Neagh), were slain.
[2] In 783 Tommaltach had to defend his position and won the Battle of Duma Achad (Dunaughey, modern County Antrim) against his internal enemies.
[3] Upon the death of Fiachnae mac Áedo Róin (died 789), King of Ulaid, the Dal Fiatach became involved in a civil feud and Tommaltach made himself King of Ulaid.
His grandson Lethlobar mac Loingsig (died 873) was also a King of Ulaid.