Denmark was the dominant Nordic power in the late tenth century. Southern Norway and the Oslo Fjord sometimes fell under direct Danish rule, and Haakon Sigurdsson governed the rest as a vassal of King Harald Bluetooth. In practice, Haakon operated with considerable independence, but the relationship had a breaking point: religion. Haakon was a committed believer in the Norse gods at a time when Harald Bluetooth was aggressively Christianizing his domain. Around 975, when Harald attempted to impose Christianity on his Norwegian vassal, Haakon broke his allegiance. The timing was shrewd. Harald had recently suffered defeat at the hands of Otto II, Holy Roman Emperor, in 974, and his weakened position gave Haakon an opening to act.

Harald Bluetooth's response came in the form of the Jomsvikings, a legendary band of professional warriors based at the fortress of Jomsborg, whose exact location remains uncertain but is traditionally placed on the southern coast of the Baltic. Whether the Jomsvikings were a historical military order or a later literary invention has been debated by scholars, but the sagas present them as elite fighters bound by a strict code. The fleet they sent against Haakon represented Denmark's attempt to reassert control over Norway by force. The two navies met in Hjorungavagr, a bay surrounded by the islands and headlands of the Sunnmore coast, where the narrow waters would have favored close combat between ships lashed together in the Viking fashion.

The details of the battle come filtered through saga literature rather than contemporary record, though several skaldic poets of the period allude to the fight. Thorthr Kolbeinsson and Tindr Hallkelsson composed verses that reference the engagement, and the Icelandic skald Einarr Helgason celebrated Haakon's triumph in the poem Vellekla. The Jomsvikingadrapa, by Bjarni Kolbeinsson, honors the fallen Jomsvikings. Heimskringla, Saxo Grammaticus's Gesta Danorum, and the Jomsvikinga saga all describe the battle, though they do not agree on every detail. What the sources share is the essential narrative: Haakon's fleet won a convincing victory, the Jomsvikings were broken, and Danish ambitions over Norway were put to rest for a generation.

The Battle of Hjorungavagr sits in the uncertain territory between documented history and literary tradition. Scholarly convention dates it to 986, supported by Saxo Grammaticus's placement of the battle during Harald Bluetooth's lifetime. The battle is described in the kings' sagas and has been the subject of poems, plays, and local tradition for a thousand years. A national monument now stands at Hjorungavag on the Sunnmore coast, marking the probable site. The bay itself, wherever precisely it lies among the islands, would have been typical of the landscape that shaped Viking naval warfare: sheltered enough for fleets to gather, narrow enough to force engagement, surrounded by mountains that turned sound back on itself. Haakon Sigurdsson remained Norway's sole ruler until his death around 995, and Denmark's claim was not pressed again until the Battle of Svolder, roughly fourteen years after the longships clashed in Hjorungavagr.