The public prosecutor alleged that Sadi Bugingo took part in the killings of some 2,000 people mainly belonging to the Tutsi ethnic group, according to charges read out in the Oslo District Court.
"He participated in killing and transported armed killers and internally displaced people to places where the internally displaced people were killed," court papers said, singling out three prolonged attacks during April 1994 in Kibungo, eastern Rwanda.
"He strengthened the killers' motivation to take lives with his presence," the charge sheet said.
The accused, appearing quiet and collected in court, denied all charges speaking through a Kinyarwanda interpreter. If found guilty he faces a maximum sentence of 21 years in prison.
Bugingo, 47, arrived in Norway in 2001 to join his family. He was arrested last year in the western city of Bergen, where he had been employed as a cleaner.
The trial is scheduled to last several months with a verdict expected in early 2013.