Gissur played a major role in the period of civil war which is now known as Age of the Sturlungs: he fought alongside Kolbeinn the Young against the forces of Sturla Sighvatsson of the Sturlungar clan in the Battle of Örlygsstaðir in 1238 and led the force of men who murdered saga-writer Snorri Sturluson in 1241, at the behest of Haakon IV, King of Norway.
Gissur was crucial during the civil war era called Age of the Sturlungs: he fought alongside Kolbeinn the Young against Sturla Sighvatsson's forces in the Battle of Örlygsstaðir in 1238 and directed the group that killed saga-writer Snorri Sturluson in 1241, as ordered by Haakon IV, King of Norway.