Adam Idrisovich Magomadov, a 23-year-old Russian of Chechen origin, and Hasan Ahmed, a 46-year-old Norwegian of Pakistani origin, were convicted of belonging to IS and of "terror conspiracy."
The two men, who had been living in southeastern Norway, travelled together to Syria in August 2014, a little more than a month after the IS declared a caliphate in an area straddling Iraq and Syria.
While there, the two took part in IS training programmes, vowed allegiance to the group, and bore weapons in its name, the court found.
Magomadov was handed a heavier sentence because he stayed in Syria longer. The court found it likely that he had taken part in combat, that he had maintained ties with IS after returning to Norway, and that he, like his co-accused, planned to return to Syria.
Ahmed, whose son Ishaq was also sentenced to eight years in prison in Norway last year for joining IS, will appeal the conviction, while Magomadov had not yet decided, their lawyers told public broadcaster NRK. Their sentences were in line with those requested by the prosecution.