A Paris court convicted Le Pen and two dozen National Rally (RN) party members of embezzling EU funds last week and imposed a sentence that will prevent her from standing in France's 2027 presidential election unless she can get the ruling overturned within 18 months.
"We will follow Martin Luther King as an example," Le Pen said in a video appearance for Italian Matteo Salvini's anti-immigration Lega party, which was holding a meeting in Florence on Sunday.
"Our fight will be a peaceful fight, a democratic fight. We will follow Martin Luther King, who defended civil rights, as an example."
Le Pen supporters waved French flags and chanted "we will win" as they gathered in central Paris on Sunday afternoon for a peaceful protest, which could give an indication of how much popular backing there is for her accusations that prosecutors in the case sought her "political death".
Pensioner Marie-Claude Bonnefont, 79, said she was against "this parody of a decision against Le Pen".
"One should really question the impartiality of the judges," another protester, political science student Typhaine Quere, told Reuters.
There was no immediate police estimate of attendance at Sunday's protest, but organisers said about 15,000 people had gathered.
The court's ruling was a massive blow for Le Pen, 56. The National Rally chief is one of the most prominent figures of the European far right, and a front-runner in polls for France's 2027 election.
Le Pen has appealed the court's decision, and she vowed on Sunday to use all the tools and legal means to be able to run in 2027. The court has said it will issue a ruling on the appeal in the summer of 2026.
An opinion poll by Elabe on Saturday showed Le Pen was still favourite to win the first round of the presidential vote with between 32 per cent and 36 per cent support, ahead of former Prime Minister Edouard Philippe, who was polled at between 20.5 per cent and 24 per cent.
But attacks by Le Pen and her allies over the "tyranny of judges" have not gained traction, even among some of her supporters, particularly after the lead judge in her case was put under police protection following death threats.
Most French people do not see any problem with the court's decision.
Some 65 per cent of respondents said they were "not shocked" by the verdict and 54 per cent said Le Pen was treated like any other defendant, according to an Odoxa poll.
Across the city, at Place de la Republique, leftist party supporters flocked to a counter-demonstration to protest Le Pen's attacks on the French state.
Centrist politicians including two former prime ministers, Gabriel Attal and Philippe, also gathered on Sunday to show a united front against the RN.
"Let us maintain this commitment to the morality of political life and to our institutions at a time when they are being challenged by the far right, which is gathering today to attack our judges, to attack our institutions," Attal said.
