The 68-year-old former gynaecologist was on Wednesday found guilty of genocide, crimes against humanity and participation in a conspiracy to prepare these crimes.
His lawyers said they planned to appeal the verdict.
The public prosecutor had sought a sentence of 30 years, arguing that the “sum total” of his choices showed “the traits of a genocidaire”.
Munyemana was accused of helping draft a letter of support for the then interim government, which encouraged the massacre of the Tutsi minority.
He was also accused of helping set up roadblocks to round people up and keeping them in inhumane conditions in local government offices before they were killed in the southern Rwandan prefecture of Butare, where he lived at the time.
During the trial, Munyemana repeatedly disputed the accusations, claiming he had been a moderate Hutu who had instead tried to “save” Tutsis by offering them “refuge” in local government offices.
In 2011, a French court charged the father-of-three as genocidal, Sosthene Munyemana, on suspicion of taking part in the 1994 genocide.
Munyemana was close to Jean Kambanda, the head of the interim government established after the plane carrying then-president Juvénal Habyarimana was shot down by a missile in 1994.
The trial at the Assize Court in Paris came nearly three decades after a complaint was filed against Munyemana in the southwestern French city of Bordeaux in 1995.
It is the sixth trial in France of an alleged participant in the massacres, in which about 800,000 people, most of them ethnic Tutsis, were slaughtered over 100 days by Hutu soldiers and extremist militias, according to UN figures.
France has been one of the top destinations for those implicated in the Rwandan slaughter fleeing justice at home.
Rwanda under President Paul Kagame has accused Paris of being unwilling to extradite genocide suspects or bring them to justice.
Since 2014, France has tried and convicted six figures including a former spy chief, two ex-mayors and a former hotel chauffeur.
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