The Southern Uí Néill (Irish: Uí Néill an Deiscirt, IPA:[ˈiːˈnʲeːl̪ʲˈanˠˈdʲɛʃcəɾˠtʲ]) were that branch of the Uí Néill dynasty that invaded and settled in the Kingdom of Mide and its associated kingdoms.
In the initial decades two sons of Niall Noigiallach, Lóegaire and Coirpre and their immediate descendants led the dynasty. However, after the murder of Túathal Máelgarb in about 549, it was left to another branch of the family descended from another of Niall's sons – Conall Cremthainne – to continue Uí Néill expansion and consolidate their position. No descendants of either Lugaid mac Lóegairi or Túathal Máelgarb are recorded, and it is not unlikely that they were either erased from the genealogical record, or indeed literally erased from history.