The appeals court in Paris confirmed the punishment, which also included a €10,000 ($13,000) fine, imposed in 2008 after Le Pen was found guilty of denying a crime against humanity.
Le Pen, who had made the remarks in an interview with a far-right magazine in 2005, was not present for the court ruling.
Le Pen had told Rivarol magazine that "in France, at least, the German occupation was not especially inhumane, even if there were a number of excesses -- inevitable in a country of 550,000 square kilometres".
Le Pen said he would appeal the ruling to France's Court of Cassation, the country's court of last resort, and linked Thursday's decision with the French presidential election in April.
"I will make an appeal in cassation against this decision, which I'm not surprised comes during the election period," Le Pen told AFP, accusing the courts of "opportunism".
The far-right leader handed over the reins of his National Front (FN) party to his daughter Marine last year and she is currently in third place in opinion polls, with around 20 percent, ahead of the presidential vote.
Le Pen, who founded the FN in 1972, had been convicted of racism or anti-Semitism on a number of previous occasions. In 1987 he described the Nazi gas chambers as a "detail of history".
With the help of the Vichy government during World War II, the German authorities deported more than 70,000 French Jews to death camps, and thousands of French civilians died in reprisals by the German army.
In 2002 Le Pen shocked observers by making it through to the second round of France's presidential election.