Irpa appears in chapter 21 of the Jómsvíkinga saga, which focuses on the late 10th century Battle of Hjörungavágr between the fleet of the Jomsvikings under Sigvaldi Strut-Haraldsson and the fleet of Haakon Sigurdsson and Sweyn Haakonsson. Haakon calls a meeting during a lull in the fighting, and says that he feels that the tide of the battle is going against his allies and him. Haakon then goes to an island called Primsigned, north of Hjórunga Bay. On the island, Haakon falls to his knees, and, while looking northward, prays to what is described as his patron goddess, Þorgerðr Hölgabrúðr. According to the saga, Þorgerðr repeatedly refuses his offers, but finally accepts the blót of his 7-year-old son. Haakon's slave, Skopti, slaughters the boy. Haakon returns to his fleet and presses his men to engage in an attack, and commends his men to ("Þorgerðr" is here anglicized as "Thorgerd"): Press the attack all the more vigorously, because I have invoked for victory both the sisters, Thorgerd and Irpa. Haakon enters his ship, the fleet rows forward for the attack, and battle ensues. The weather becomes thick in the north, the clouds cover the sky, daylight becomes sparse, thunder and lightning ring out, and it begins to rain. The Jomvikings fleet fights facing the storm and cold, and they have trouble standing due to the heavy wind. The Jomsvikings throw weapons, missiles, and stones at Haakon's fleet but the winds turn their projectiles back at them. Hávard the Hewing, in the fleet of Haakon, first spots Þorgerðr there and then many others see her. The wind wanes and the men witness arrows flying from the fingertips of Þorgerðr, each arrow killing a man of the Jomsviking fleet. The Jomsvikings tell Sigvaldi that although they are no longer fighting men alone, they will still do their best. The storm lessens again and once again Haakon invokes Þorgerðr. The saga describes this attack: And then it grew dark again with a squall, this time even stronger and worse than before. And right at the beginning of the squall Hávard the Hewing saw that two women were standing on the earl's ship, and both were doing the same thing that Thorgerd had done before. Sigvaldi tells his men to retreat, and reasons that this is not what he vowed to fight, especially since there are now two women, whom he refers to as "ogresses"