France's far-right National Rally (RN) leader Marine Le Pen has called a court ruling banning her from running for office for five years a "witch hunt".
"I won't give up," she told thousands of flag-waving supporters in Place Vauban, close to the Eiffel Tower in Paris on Sunday.
She was on Monday found guilty of helping to embezzle €2.9m (£2.5m) of EU funds between 2004 and 2016 for use by her party. Le Pen has appealed.
At the rally on Sunday she claimed the ruling was a "political decision", adding: "We are not asking to be above the law, but to not be below the law."
Bardella, the president of the RN party, told the rally on Sunday that the court ruling was "a direct attack on democracy and a wound to millions of patriotic French people".
He said he did not want to "discredit all judges" but claimed that the judgement against Le Pen was aimed at "eliminating her from the presidential race" in 2027.
In reply on Sunday Gabriel Attal, the head of French President Emmanuel Macron's centrist Renaissance party, responded by saying "you steal, you pay".
Attal also denounced "unprecedented interference" in France's affairs, pointing to support for Le Pen from several right-wing leaders, including Italian Prime Minister Giorgia Meloni and Hungary's PM Viktor Orban.
US President Donald Trump called her conviction a "very big deal".
A poll by BFMTV after Monday's ruling showed that many people in France believe that justice was service in the Le Pen case without bias - 57% according to the poll.
The Paris Court of Appeal said on Tuesday it should be able to provide a decision on the case by the summer of 2026 - several months before the 2027 presidential election.
Le Pen was gearing up to run for the presidency for a fourth time and had a good chance of winning.
On top of the ban on running for public office, Le Pen was also handed a €100,000 (£82,635) fine and four-year prison sentence, of which two years will be suspended.
This will not apply until the appeals process is exhausted, which could take several years.
RN spokesperson Laurent Jacobelli said that although the party would fight to have Le Pen as candidate, its 29-year-old president, Bardella, was "the most naturally legitimate" alternative.
Bardella has steered clear of being drawn into the discussion at this stage, refusing to say whether he was National Rally's "plan B" and saying after the ruling that the French should be "outraged" by the sentence.
However, a poll published a day before Le Pen was sentenced showed that around 60% of RN voters would back Bardella over Le Pen at the presidential election if he were to run.
France's President Macron is not entitled to stand for another term at the next presidential election.