His father was king of Norway from 1142 to 1157, ruling as co-ruler with his brothers, Inge Haraldsson and Sigurd II Munn.
Eystein II was killed in 1157 during the power-struggle against his brother, Inge, in an early stage of the civil war era in Norway.
The Birkebeiner took the city of Trondheim and proclaimed Eystein to be king at the Øretinget Thing by the mouth of the river Nidelva in during 1176.
The background for these conflicts were the unclear Norwegian succession laws, social conditions and the struggle between Church and King.
The primary sources of information regarding Øystein Øysteinsson Møyla are Fagrskinna, Heimskringla and Sverris saga.