Sosthene Munyemana was found guilty of crimes including genocide and crimes against humanity.
He was accused of organising torture and killings in the genocide, in which 800,000 people were killed between April and June 1994.
It took French prosecutors 28 years to bring the case to trial.
In 1994, Munyemena was a gynaecologist in Butare, southern Rwanda, and was accused of helping set up roadblocks to round people up, and keeping them in inhumane conditions in local government offices before they were killed.
He was also accused of drafting a widely-distributed letter encouraging the massacre of Tutsis, which prosecutors said was used as justification for future attacks.
Most of those killed in the genocide were from the minority Tutsi ethnic group, and opponents of the extremist Hutu government.
During the trial, Munyemana, who moved to France in 1994, repeatedly disputed the accusations against him, claiming he had been a moderate Hutu trying to save Tutsis by offering them refuge in local government offices.
The prosecutor had sought a 30-year jail sentence during the six-week trial in Paris.
Reading the verdict, the judge said Munyemana was part of a group that "prepared, organised and steered the genocide of the Tutsis… on a daily basis".
After arriving in France in September 1994 - where his wife was already living - Munyemana lived in the country's southwest, and worked as a doctor. He recently retired.
A complaint was filed against him in Bordeaux in 1995.
* Rwanda: How the genocide happened
* Rwanda's 100 days of slaughter
Munyemana was a close associate of Jean Kambanda, who was interim prime minister at the height of the 1994 killings.
Kambanda is currently serving a life sentence in Mali, imposed by a United Nations war crimes tribunal for his role in the genocide.
The genocide was sparked by the death of Rwandan President Juvenal Habyarimana when his plane was shot down above the airport in Kigali, Rwanda's capital, on 6 April.
Mr Habyarimana was from Rwanda's Hutu ethnic majority, and while exactly who killed the president has not been established, the presidential guard in Kigali immediately initiated a campaign of retribution.
Leaders of the political opposition were murdered, and almost immediately, the slaughter of Tutsis and moderate Hutus began.
Within hours, recruits were dispatched all over the country to carry out a wave of slaughter that saw 800,000 people killed in 100 days.
Source: BBC News