Laurent Serubuga, around 75-years-old, was apprehended near the northern French city of Cambrai under an international arrest warrant issued by Rwanda, lawyer Thierry Massis said.
Serubuga was being held in detention and a hearing has been scheduled for , but may be postponed to a later date, the lawyer said.
Serubuga was a deputy Rwandan army chief of staff during the April-July genocide in 1994 in which an estimated 800,000 people, mostly minority Tutsis, were killed by the ethnic majority Hutus.
Alain Gauthier, who heads Rwandan victims' group CPCR, said Serubuga's arrest was "excellent news".
"Colonel Serubuga had as much responsibility in the genocide as colonel (Theoneste) Bagosora," he said, referring to the most high-profile figure condemned by the International Criminal Tribunal for Rwanda.
Bagosora, described by the prosecution as the mastermind of the genocide, was sentenced to 35 years in prison in 2011.