Sigurd Magnusson (1180 – 3 April 1194) was a Norwegian nobleman who campaigned against King Sverre of Norway during the Civil war era in Norway.
Sigurd Magnusson was the son of King Magnus V of Norway and Gyrid Aslak. Sigurd Magnusson was the only publicly acknowledged son of King Magnus. Several years of warfare with Sverre Sigurdsson had ended with the defeat and death of King Magnus in the Battle of Fimreite (Slaget ved Fimreite) in 1184. In the aftermath, groups made up principally of the Norwegian aristocracy, clergy and merchants was formed to depose King Sverre.
The young Sigurd was proclaimed to be King of Norway in 1193 at the Haugating near Tønsberg. As the son of Magnus Erlingsson, Sigurd was the nominal king supported by the so-called Isle Beards (Øyskjeggs). The real leader was Hallkjell Jonsson, who had been a son-in law of Erling Skakke as well as the brother-in-law of King Magnus. With Harald Maddadsson, the Earl of Orkney, Hallkjell gathered most of his men on Orkney and Shetland, hence the name of the group. After establishing themselves in Viken, the Øyskjeggs sailed on to Bergen. Although they occupied the city itself and the surrounding regions, a force of Birkebeiners held on in the fortress of Sverresborg.
In the spring of 1194, King Sverre sailed south to confront the Øyskjeggs. The two fleets met at Florvåg on Askøy, an island just north of Bergen. King Sverre and his force confronted Sigurd Magnusson and the Øyskjeggs. King Sverre came to Gravdal with a vast fleet, which rowed over to Florvågøya. On the morning of Palm Sunday, 3 April 1194 the battle took place. Here the battle experience of the Birkebeiner veterans proved to be decisive. Hallkjell fell with most of his men. King Sverre won, but around 2,500 soldiers were killed in the bloody battle.