Kristian Michelsen, from a town near Trondheim, had the sentence handed down in November shortened by three months at the Borgarting Court of Appeal.
Defence lawyer Elisabeth Myhre told Dagbladet that Michelsen was “very disappointed” by the judgement.
Prosecution lawyer Frederik Ranke had called for a tougher nine-year sentence, arguing that of all the Norwegian fighters to return from Syria, Michelsen had spent the longest time with IS.
“It is an aggravating circumstance that over this period he had no change of heart. He sought IS voluntarily,” he said in court. “It should not be seen as a mitigating circumstance that he could not get himself out.”
In the trial, Myhre's colleague Trygve Staff argued that Michelsen had only actively borne arms for Islamic State for a few months in the winter and spring of 2015, arriving in Syria in November 2014 and starting to draw up plans to escape the following April.
Michelsen finally escaped from IS a year later in April 2016, but was arrested in Turkey and imprisoned, before being deported to Norway later that year.
Staff's colleague Elisabeth Myhre told Dagbladet: “He has the whole time been open about being in Syria, and about staying in an IS-controlled area, but he believes he has not done anything punishable under criminal law.”
According to Norway's PST security services, about 100 Norwegian warriors travelled to Syria and Iraq, 30 of whom have been killed, 40 returned to Norway, and about 30 still in Syria or Iraq.