He was the son of Olof Trätälja of the House of Yngling. His father was sacrificed to Odin by the Swedish settlers in Värmland because of a famine. Some Swedes, however, realised that the famine was brought by overpopulation and not by the fact that the king had been neglecting his religious duties.
Consequently, they resolved to cross the Ed Forest and settle in Norway and happened to end up in Soleyar where they killed king Sölve and took Halfdan prisoner. The Swedish expatriates elected Halfdan king as he was the son of their old king, Olof. Halfdan subjugated all of Soleyar and took his army into Romerike and subjugated that province as well.
Halfdan conquered a large part of Hedemark, Toten, Hadeland and a part of Vestfold. When his brother Ingjald Olofsson died, he inherited Värmland. Halfdan died of old age in Toten and was transported to Vestfold where he was buried under a mound in Skiringssal.