Sadi Bugingo, who is wanted by the Rwandan authorities, stands accused of having played a role in two massacres.
Bugingo, who arrived in Norway in 2002, was arrested in the western city of Bergen in May last year at the request of Rwanda and has been in detention since. He denies the accusations against him.
"It's the first time that we are prosecuting someone for genocide," said prosecutor Petter Mandt. "From that point of view it is a very unusual affair."
He wanted a public trial so that people would know that Norway was not a refuge for these kind of criminals, he said.
The trial will focus on Bugingo's alleged involvement in two massacres of people who were hiding from militia. Some of those killed were dragged from their hospital beds.
Mandt said the trial was due to open on September 25th and hearings expected to last three months. The verdict is expected in February or March.
If convicted, Bugingo faces up to 21 years in jail, the maximum term possible at the time of the alleged crime. But it can be prolonged indefinitely if the person convicted is considered to be still dangerous.
A 30-year prison sentence for genocide was introduced into the criminal code in 2005, but cannot be applied retroactively.
The 1994 genocide by Rwandan Hutus against the Tutsi minority and some Hutu moderates claimed 800,000 lives in 100 days, according to UN figures.