Pascal Simbikangwa, 54, appeared in a Paris court on Tuesday on the first day of the long-awaited trial, in which more than 50 prosecution witnesses are expected to describe the ex-soldier's alleged role in arming and directing Hutu killers.
Human rights activists and journalists from Rwanda crowded the chamber to follow the trial. Simbikangwa denies the charges brought against him.
"We're not here in our own name, but in the name of the million victims who were exterminated in Rwanda in 1994," Alain Gauthier, co-founder of a Rwanda victims' group that is party to the case, told journalists.
Long considered a safe haven for ringleaders of the 1994 Rwanda genocide, France lags behind neighbors like Belgium, Switzerland and Germany that have already brought suspects living on their soil to justice.
According to a 1996 French law, Rwandans suspected of being involved in the genocide can be tried in a French court
Fined a decade ago by the European Court of Human Rights for dragging its heels on cases filed since 1995, France created a special genocide investigation unit two years ago that has studied some 20 legal complaints against alleged perpetrators.
A paraplegic since 1986, Simbikangwa is charged with complicity in genocide and in crimes against humanity and risks a life sentence with a mandatory 22 years behind bars. He was arrested in hiding on the French Indian Ocean island of Mayotte in 2008.
The three-month killing spree in 1994 by Hutu extremists targeted ethnic Tutsis, but moderate Hutus were also caught in the wave of violence that followed the fatal downing of a plane carrying Rwandan President Juvenal Habyarimana.
Following the genocide, current President Paul Kagame accused France of training and arming the Hutu militias, a charge Paris has always denied, spurring a diplomatic freeze.
Simbikangwa's trial represents a major step in a fragile rapprochement between the two countries and French diplomats say in private that an acquittal would be a step backward.
French President Francois Hollande hopes to strengthen diplomatic and economic ties with the east African nation, viewed as crucial for maintaining stability in the region.
Rwanda is already embroiled in Democratic Republic of Congo, its neighbor, which Kigali says shelters Hutu militia who fled after Rwanda's genocide. U.N. experts accused Kigali of backing the Tutsi-led M23 rebels in eastern Congo who finally signed a peace deal with the Congolese government in December.
Simbikangwa, a devoted ally of Habyarimana, is accused among other things of whipping up anti-Tutsi sentiment through radio and television stations which the prosecution says he helped finance.
In a rare step, the trial will be filmed with recordings available at the trial's conclusion.
(Writing By Alexandria Sage; Editing by Tom Heneghan)