When the tidings of King Olaf's death had gone abroad, the inhabitants of Viken acknowledged his son, Magnus, as king, while the TrÖnders made haste to proclaim his nephew, Haakon Magnusson. The country was, accordingly, once more divided; two thirds, including TrÖndelag, the Oplands, and all the northern shires, belonging to Haakon, and about one third to Magnus. The latter was scarcely prepared to find a rival to the throne in his cousin, who during his father's long reign had given no evidence that he cherished such an ambition. Only ignorance, on his part, of Haakon's intentions can explain his departure on an adventurous expedition to Scotland. The restless, warlike spirit of his grandfather dwelt in him, and he had chafed under the restraint which his father's peaceful policy imposed upon him. Now that he was free, he could afford to lose no more time in dallying. He therefore started, as soon as he had his hands free, on a wild-goose chase for glory; helped the Scottish king, Donald Bane, in his warfare against Eadgar the Etheling and his brother, Malcolm's children; asserted (apparently with success) his claim to the Scottish isles, which, during Harold Hard-Ruler's reign, had made themselves independent; aided the Irish King Muirkertach against the earl, GudrÖd Meranagh; and finally returned home in the summer of 1094 to find two thirds of his kingdom in the hands of a rival. He sailed directly to Nidaros with seven ships and took up his abode in the new royal mansion, resolved to make the TrÖnders feel the weight of his wrath. Haakon and his foster-father, Thore of Steig, also hastened to the city and put up at the old royal mansion. The relation between the two parties was strained, and every day people expected an outbreak of hostilities. Finally Haakon opened negotiations with his cousin, offering to divide the kingdom with him in equal parts; but Magnus repelled his overtures, refusing to recognize his title to any share in the government. Suddenly, in the middle of the night (February, 1095), Magnus had great fires made around the city, and Haakon's men, expecting an attack, seized their arms and rushed into the streets. No attack was, however, made, and both parties left the city without any hostile collision. Haakon, in crossing the Dovre Mountain on snow-shoes, was taken ill and died.

One would have supposed that the TrÖnders had now no longer any pretext for persevering in their opposition to Magnus. But apparently they both hated him, and feared that he would mete out severe punishments to them for the support they had given his cousin. Therefore they gave heed to the counsel of Thore of Steig, who demanded their allegiance to a pretender named Sweyn, a Dane by birth, and not related to the royal house of Norway. The rebels found many adherents in the Oplands, among whom the liegeman Egil Aaslaksson. Under the leadership of Thore and Sweyn they started out, ravaging and plundering in Nordmore and TrÖndelag. They gave the peasants the choice either to join them or have their houses burned over their heads; and there were many who preferred the former alternative to the latter. Magnus' liegeman and devoted friend, Sigurd Wool-String (Ullstreng), sent out war summons, but his force, which was quite inadequate, was utterly defeated by the rebels. He fled to Magnus, who instantly started in pursuit, captured Thore of Steig and Egil, and hanged them. Many others who had participated in the rebellion were killed or deprived of their property; and as a punishment to the TrÖnders, the laws of Sweyn Alfifasson were re-enacted.

Magnus was now undisputed master of all Norway and devoted himself with much energy to the maintenance of order by meting out relentless justice to evil-doers. To sit at home in inglorious ease, punishing rebels and marauders, was not, however, in accordance with his taste. He hated peace as much as his father had loved it. Without any special provocation he, therefore, determined to pay a second visit to Scotland and Ireland for the purpose of securely founding his dominion in those lands. It appears that he was also cherishing a plan for invading England and avenging the death of his grandfather at Stamford Bridge. Haakon Paulsson, a son of Earl Paul of the Orkneys, who came to Norway, stimulated his ambition, hoping himself in some way to profit by it. With a fleet of 160 ships and upward of 14,000 men the warlike king sailed in the spring of 1098 for the Orkneys, and thence to the Hebrides, where he harried with remorseless cruelty. He conquered also the English islands of Man and Anglesey, and made great efforts to colonize the latter island. In the summer of 1099 he returned to Norway, but managed within a year to get himself into a promising quarrel with King Inge of Sweden, one of whose provinces (Dalsland) he claimed on a flimsy pretext. He won a great victory over the Swedes at Fuxerne, and left a garrison of 360 men in a fortress which he built on an island in Lake Wener. But King Inge forced this garrison to surrender, on humiliating terms, during the winter; and Magnus, to avenge this disgrace, invaded Sweden a second time, and was defeated not far from TrollhÄttan. He came then near losing his life, but was saved by Agmund Skoftesson, who changed cloaks with him, and, starting conspicuously away from the other fugitives, drew the pursuers after him. This kind of warfare was, of course, sheer waste of life and treasure, and by the mediation of the Danish king, Erik Eiegod, peace was concluded at Konghelle, (1100). Magnus was to marry King Inge's daughter Margaret, who was to receive the disputed province as her dowry. The marriage, however, was without issue, and Dalsland became, at the death of Magnus, again a part of Sweden. Queen Margaret, because she was the bringer of peace, was called by the Norsemen, Fridkulla, i.e., the peace-maker.

It was not to be expected that Magnus should rest contented with the fame he had now gained, and turn his mind to the pursuits of peace. His sentiments in that regard are well expressed in his saying: "A king should rather strive for glory than for a long life." In his anxiety to find a pretext for war he finally, as it is told, sent a pair of his shoes to King Muirkertach, in Ireland, with the request that he should carry them on his shoulders, on Christmas Day, in the presence of the Norse ambassadors, as a sign that he recognized Magnus at his overlord. The Irish were greatly incensed at this demand; but Muirkertach, who knew something of Magnus' style of warfare, declared that he would not only carry the shoes, but that he would eat them too, rather than receive another visit from the king of Norway. This humility did not, however, save him from the dreaded visitation. Magnus had determined upon the conquest of Ireland, and forthwith sailed (1102) westward with a large fleet. After having touched at the Orkneys, he landed on Man, where he had his son, Sigurd, proclaimed king and married to Muirkertach's nine-year old daughter, Biadmuin. He fought for a while with varying success in Ulster, nominally in alliance with Muirkertach, though there is every reason to believe that the latter was only watching for a chance to destroy him. Such a chance finally presented itself, while Magnus was waiting on the coast of Ulster for a herd of cattle that had been promised him. He had gone ashore with a small part of his force in a swampy region, and was suddenly surrounded by the Irish, who had hid in the underbrush, and who, on account of their knowledge of the ground, had a great advantage. Here Magnus fell after a heroic combat, and the remnant of his army made haste to return to Norway.

Magnus was but thirty years old at the time of his death. He was a tall and well-grown man, of fine features and a commanding appearance. His surname Barefoot or Bareleg was given to him because, after his return from his first Scotch campaign, he adopted the Highland costume, wearing kilts instead of trousers.