Her party, National Rally, has given the backing a cool reception.
Spokesman Laurent Jacobelli said in an interview that the party agreed with Musk's assessment but was not seeking support from abroad.
"What matters is not the opinion of people abroad, but the opinion of the French," he said.
MEP Thierry Mariani told US news outlet Politico that the party had not asked for Musk's endorsement.
National Rally has kept a similar distance from Donald Trump, despite ideological common ground, as neither he nor Musk are popular in France, even on the right, the website notes.
The post has stoked concern in France that the world's first trillionaire could use his media platforms to campaign for Le Pen.
A foreign ministry spokesman said Musk was free to voice his opinions, but that his tools must not be allowed to tilt the election debate towards one candidate.
According to former EU commissioner Thierry Breton, the French government should ensure X's algorithms in Europe do not favour any candidate.
French daily Le Figaro described the post as an official endorsement of Le Pen, noting Musk's pattern of backing populist and far-right movements across Europe.
In 2024, he called Germany's AfD the country's "only hope", prompting CDU leader Friedrich Merz to say he could not recall a comparable case of interference in an ally's election campaign.
Musk has also backed Nigel Farage's Reform UK, branded Spain's Pedro Sánchez a "fascist" and "traitor", and supported jailed far-right activist Tommy Robinson, prompting British weekly The Economist to accuse the businessman of crossing a line by cultivating ties with European extremists.
(ał)
Source: PAP