A Paris court found 87-year-old Le Pen guilty of the charge of denying crimes against humanity.
The court rejected Le Pen's claim that he had parliamentary immunity from prosecution.
The judges ordered the verdict to be published in three newspapers and said Le Pen must also pay 10,001 euros in damages to three charities which brought the case.
Le Pen, who has been succeeded by his daughter Marine as FN leader, first made the comments about the gas chambers in 1987. He repeated them in 1997 in Germany and then in 2008 and 2009 in the European Parliament.
The comments sparked a row with his daughter, Marine Le Pen, who has tried to move the party away from its anti-Semitic and racist image.
She has expelled her father from the party amid a bitter feud.