France's far-right chief Marine Le Pen was braced for a key verdict on Tuesday that will determine if she can run in next year's presidential elections, when her party has its best chance yet of winning power.

A lower court last year sentenced Le Pen, 57, to a five-year ban from public office and two years in prison over a fake jobs scam at the European Parliament.

If the appeals court upholds that ruling, it will be a devastating blow to the three-time presidential candidate's hopes to replace outgoing centrist President Emmanuel Macron.

The decision, expected to be read out from 1:30 pm, could also find her guilty but include a shorter ban from public office and some form of house arrest.

If the sentence prevents her from campaigning, she has said she will hand over to her 30-year-old lieutenant, Jordan Bardella, the leader of their Rassemblement National (RN) party.