Sadi Bugingo, a 47-year-old Hutu who has lived in Norway since 2001, was found guilty of being an accessory to genocide for ensuring that orders issued for the killings were carried out.
He did not face any charges of having carried out any killings himself.
The 21-year-sentence demanded by prosecutors is the maximum available in Norway.
The case centred on several events in April 1994: a massacre in a municipal building, another within the grounds of a Catholic church, and on several different occasions, the killing of people who had sought refuge in a hospital.
"The murders were meticulously planned and the accused undoubtedly acted with premeditation," the three Oslo district court judges said in the ruling.
"He made sure the massacre of (Tutsi) refugees was carried out in line with plans," they said, citing numerous witness testimonies.
The court also cited aggravating circumstances, since the attacks were part of a genocide and carried out in "beastly fashion" with machetes, bats and clubs, and dead bodies were in some cases desecrated.
It also noted that the "wealthy businessman" profited from the genocide, stealing a power generator from the church among other things.
Bugingo, who had worked as a cleaner in Norway until his arrest in 2011, had pleaded not guilty when the trial opened last September.
His lawyer had called for his client's acquittal, and Bugingo immediately appealed the verdict.
Bugingo has insisted he was not present during the massacres, and claimed the witness testimonies were lies. He himself is married to a Tutsi, and told the court that he saved many Tutsis' lives during the genocide.
The court noted though that "it was not uncommon for those who participated in the genocide to also have family ties and friendships with Tutsis, and that they took advantage of their position during the genocide to protect them."
The trial was the first for genocide in the Scandinavian country.
The April 6, 1994 killing of Rwanda's Hutu president Juvenal Habyarimana triggered a genocide in which 800,000 people, mostly from the Tutsi minority, were killed, according to UN figures.