Muirgius mac Tommaltaig (died 815) was a King of Connacht from the Uí Briúin branch of the Connachta. He was the great-grandson of Indrechtach mac Muiredaig Muillethan (died 723), a previous king. The death of his father Tommaltach mac Murgail (died 774) is recorded in the annals where he is called king of Mag nAi. Muirgius was of the Síl Muiredaig sept of the Uí Briúin. He reigned from 792 to 815.