The C8 channel said it had secretly recorded Benoit Loeuillet, a National Front regional councillor in the southern region of Provence-Alpes-Cote d'Azur, using a hidden camera for a documentary about the party being screened on Wednesday.
"There was no mass murder as has been said," Loeuillet was quoted as telling the undercover reporter in an advance extract of the documentary, referring to the deaths of six million Jews in the Holocaust.
Loeuillet denied in a statement on Facebook that he had in any way questioned the reality of the Holocaust and said he had asked his lawyer to sue the documentary-makers for libel. He also said he was resigning from the National Front.
National Front Secretary-General Nicolas Bay had earlier said in a statement that, as a result of his reported comments, Loeuillet had been suspended from the National Front and would be called very soon to a disciplinary hearing to be expelled from the party.
The incident is embarrassing for the National Front whose leader, Le Pen, is tipped by polls to win most votes in the first round of the presidential election in six weeks' time, although she is predicted to lose heavily in the run-off in May.
Since taking over from her father Jean-Marie Le Pen in 2011, Marine Le Pen has sought to improve the anti-immigration party's image, making it more mainstream and distancing it from its founder's past anti-Semitism.
She had her father expelled in 2015 for renewing earlier declarations playing down the Holocaust.