The trial, which begins on Tuesday, follows a ruling last year in which a French court banned Le Pen, 57, from running for office for five years in an EU Parliament fake-jobs case involving her and other officials from her National Rally party.
The three-time presidential candidate was also sentenced to four years' imprisonment, two of which were suspended, and a fine of €100,000.
Le Pen, who has always said she is innocent, is now seeking to overturn that verdict on appeal in hopes of clearing the way for her fourth run at the Elysée.
But if the court maintains the ruling, she will be barred from standing in the 2027 poll, widely seen as her best –- and possibly last -– chance to win the country's top job.
Twelve of the accused, as well as the party itself, have appealed the verdict, including RN deputy party leader and Perpignan mayor Louis Aliot.
Another 12 people -- including one of Le Pen's sisters -- have however decided to accept their convictions without appealing. Another person convicted has since died.
The trial is expected to run until February 12, with a verdict expected this summer.
The initial ruling was a devastating blow for Le Pen and the RN, which has been ascendant in French politics in recent years.
The court found her guilty, along with 24 former MEPs, assistants and accountants and the far-right party as a legal entity, of operating a "system" from 2004 to 2016 using EU Parliament funds to employ RN employees in France.
The court put the final cost of the scheme at €3.2 million after some defendants reimbursed €1.1 million.
"These were not administrative errors or misunderstandings by MEPs (Members of the European Parliament) of confusing European rules, but misappropriations within the framework of a system set up to alleviate the party's expenses," said the court in its ruling.
Le Pen walked out of the courtroom during the sentencing, later slamming the verdict as a "political decision".
The judges defended the ruling to bar her from running, saying elected officials should not benefit from "preferential treatment" and citing the risk of reoffending.
The news sparked shockwaves in France but also in certain quarters around the world, with the likes of President Donald Trump, his billionaire adviser Elon Musk and the Kremlin expressing concern.
According to the German weekly Der Spiegel, the Trump administration is allegedly considering sanctions against the judges of the Paris Criminal Court who convicted Le Pen last March.
But a US official on Thursday denied that Washington was considering taking such action.
"The purported leak is stale and false," US Under Secretary of State for Public Diplomacy Sarah Rogers wrote on X.
Le Pen took over the former National Front (FN) from her father Jean-Marie Le Pen in 2011 and has since sought to clean up the party's image. Her father, who died in January, was often accused of making racist and anti-Semitic comments.
Her legal troubles may leave the field open for her top lieutenant, Jordan Bardella, the 30-year-old head of the RN, to run for president in her place.
An Odoxa-Mascaret poll in November projected that Bardella would win the second round of elections, irrespective of who stood against him.
Incumbent President Emmanuel Macron cannot run again because of a constitutional two-term limit.
The country has been battling a deep political crisis since Macron called snap elections in 2024 that were intended to consolidate his power but instead resulted in a hung parliament and more seats in the chamber for the far right.
Le Pen last year called on the president to again dissolve parliament, adding that it would be "wise" for him to resign, but Macron said last week he would work until the "last second" of his mandate.
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