He and Magnus became the joint ruler of Norway in 1046

One of the interesting facts about Harald Hardrada is that he and Magnus became the joint ruler of Norway in 1046. Seeking to regain the kingdom lost by his half-brother Olaf Haraldsson, Harald set out in early 1045 from Novgorod (Holmgard) towards Staraya Ladoga (Aldeigjuborg), where he obtained a ship. His trek took him through Lake Ladoga, the Neva River, the Gulf of Finland, and the Baltic Sea. He landed in Sigtuna, Sweden, around the end of 1045 or the beginning of 1046. According to the skald Tjodolv Arnorsson, when he landed in Sweden, his ship was unstable due to its heavy load of gold. In Harald's absence, Norway's throne had been restored to Magnus the Good, Olaf's illegitimate son. Harald may have been aware of this, and it is possible that this is why Harald desired to return to Norway in the first place. Magnus's position as the king had been assured since Cnut the Great's sons had decided to flee Norway and fight over England, and his sons and successors Harold Harefoot and Harthacnut had died young. During his eleven-year reign, no domestic threats or insurrections were documented. After Harthacnut's death, which left the Danish throne vacant, Magnus was also chosen to be King of Denmark, and he defeated the Danish royal pretender Sweyn Estridsson.

When Harald learned of Sweyn's defeat at the hands of Magnus, he joined forces with his fellow exile in Sweden (who was also his nephew), as well as the Swedish king Anund Jacob, and the three joined forces against Magnus. Their first military adventure was a raid on the Danish shore. The goal was to impress the people by demonstrating that Magnus provided little protection, prompting them to submit to Harald and Sweyn. Magnus deduced from their behavior that their next target would be Norway. Harald may have intended to be crowned king of his father's minor realm before claiming the rest of the country. In any case, the people were unwilling to rally against Magnus, and upon learning of Harald's plans, Magnus returned to Norway with his entire army. Instead of fighting his uncle, Magnus' counselors advised him not to, and a solution was negotiated in 1046 in which Harald would rule Norway jointly with Magnus. Notably, Harald was also forced to agree to share half of his riches with Magnus, who was essentially bankrupt and in desperate need of finances at the time. Harald and Magnus held separate courts and stayed to themselves during their brief co-rule, and their sole known interactions nearly ended in physical fights.