Pascal Simbikangwa, a former Rwandan intelligence chief, was found guilty of complicity in the 1994 genocide and sentenced to 25 years in prison.
He's the first genocide suspect to be tried in France, which has long been accused of being too slow to bring perpetrators to justice. The prosecution had called for life-imprisonment.
After more than 11 hours of deliberation, a guilty verdict was finally handed down to the 54 year old, former spy chief.
Throughout the six-week long trial, Simbikangwa repeatedly maintained he was innocent, even claiming he'd not seen a single corpse during the three-month wave of violence, sparked after the plane of President Juvenal Habyarimana, a Hutu, was shot down.
In just one hundred days, 800, 000 people were killed, mostly Tutsis. Simbikangwa tried to minimise his role in the genocide, but the court heard how he supplied weapons and gave orders to extremist Hutus.
He was thus found guilty of complicity and crimes against humanity and sentenced to 25 years in prison.
The prosecution had wanted him imprisoned for life, whilst the defence requested he be acquitted, arguing the trial was politically motivated.
The trial was closely watched in France, long accused of being too slow to prosecute perpetrators of genocide.
The guilty verdict could set a precedent for other war criminals to face justice.
Interwiew with Rwanda Justice Minister, Johnston Busingye
It's an important day for French justice, which for 20 years has shielded genocide suspects