The verdict, to be delivered on Tuesday, could reshape the 2027 contest to replace President Emmanuel Macron if it forces the popular Le Pen out of the picture.
The constitution prevents Macron seeking a third consecutive term.
Le Pen, 57, is appealing a March 2025 conviction that found her and other members of her National Rally party guilty of misusing European Parliament funds by paying party staff with money intended for EU parliamentary assistants between 2004 and 2016.
The lower court sentenced her to prison time, suspended pending appeal, and imposed a five-year ban on holding elected office.
Le Pen has denied any wrongdoing and still hopes to mount a fourth bid for the presidency.
But a verdict that upholds a lengthy ban could make that impossible and suspend her career that has transformed the National Rally into a major political force.
Such a verdict could also reverberate on the European Union, by sidelining a fierce critic of the 27-nation bloc.
If she is barred, her protege Jordan Bardella would replace her.
Bardella, 30, is the president of the anti-immigration, EU-sceptic National Rally.
Other outcomes also are possible.
The appeals court could still find Le Pen guilty but reduce the ban on holding elected office to two years or less, or impose no ban at all.
A ban of two years or less would expire before the first round of the French presidential election, scheduled in April 2027.
But that does not automatically mean Le Pen would run.
She has said that if the court imposes other constraints that make campaigning difficult, she might decide not to run.
That could include any prison sentence, electronic monitoring or other judicial restrictions.
"If I'm allowed to be a candidate but am effectively prevented from campaigning freely, then you understand that wouldn't be possible," Le Pen said in an interview.
Prosecutors asked the appeals court to sentence Le Pen to four years in prison, including three suspended, in addition to a ban on holding elected office for five years.
They accused Le Pen of being at the head of a "system" meant to "siphon off" EU public funds to the benefit of her party.
Le Pen could still appeal to the Court of Cassation, France's highest court, but it's unclear whether judges would suspend the sentence pending a final ruling.
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