Muiredach Muillethan mac Fergusso (or Muiredach Mag Aí) (died 702) was a King of Connacht from the Uí Briúin Aí branch of the Uí Briúin.
The annals report that his father Fergus (Muirgius) had been killed in 654 by the Uí Fiachrach Aidhne.
[4] The Annals of Tigernach report a reign of 696-702 for Muiredach as king of Connacht succeeding Fergal Aidne mac Artgaile (died 696).
He was married to Cacht of the Corco Cullu (a minor tribe in Mag nAí), daughter of the slayer of his grandfather Rogallach.
[6] He was the ancestor of the Síol Muireadaigh of Connacht and his known sons were Indrechtach mac Muiredaig Muillethan (died 723) and Cathal mac Muiredaig Muillethan (died 735), both future kings of Connacht.