At the funeral feast of Harald Bluetooth, Jarl Sigvaldi swears an oath on his father's memory to go to Norway and kill or drive away Haakon Jarl.

In order to win Astrid, the daughter of the Wendish chieftain Burislav, he promised to liberate the Wends of the tribute they had to pay to the Danes. He fulfilled his promise by sailing to Zealand where he sent the message to Sweyn Forkbeard that he had important tidings, but had fallen ill and could not come in person to bring them to him. As Sweyn was curious, he went aboard Sigvaldi's ship and was captured by the Jomsvikings. To be liberated the Danish king had to grant independence to both the Jomsvikings and to the Wends, in addition to paying a king's ransom.

At his father Strutharald's funeral, Sigvaldi was advised by Sweyn to attack Norway and to depose Haakon Jarl. This promise led to the Battle of Hjörungavágr in 986, from which Sigvald fled with disgrace.

In 1000, Sigvaldi proved to be treacherous at the Battle of Swold, by luring Olaf Tryggvason to the battle and by deserting him in the heat of battle.

no:Sigvalde jarl sv:Sigvald Jarl