The Kings of Sliabh Lugha were rulers of the district of Sliabh Lugha, located in what is now County Mayo.
The Sliabh Lugha area was originally known as Gailenga but by the 12th-century called Sliabh Lugha. Its rulers were the Ó Gadhra, whose ancestors were Kings of Luighne Connacht, an over-kingdom of which Gailenga/Sliabh Lugha was the southern part. The northern area, lying in south-west County Sligo, retained the name Luighne.
After the Anglo-Norman conquest of Connacht, it was known as the Barony of Gallen, and ruled by the clan Mac Siúrtáin till early 1600s.