He must have been born some time before 1155, when his father was killed in a battle with his half-brother King Inge I of Norway.
Sigurd was fostered by Markus of Skog in Ringsaker apparently in Hedmark, due to which his nickname was Markusfostered.
In 1163, Sigurd and his foster-father were captured by supporters of Jarl Erling Skakke and Magnus V of Norway, who killed them in Bergen on 29 September 1163.
The Birkebeiner were formed in 1174 around Øystein Møyla, who was proclaimed to be king at the Øretinget Thing by the mouth of the river Nidelva in Trondheim during 1176.
The background for these conflicts were the unclear Norwegian succession laws, social conditions and the struggle between Church and King.