Centerist Emmanuel Macron, who wants to deregulate the economy and deepen EU integration, has a 23-26 percentage point lead over far-right candidate Le Pen in the opinion polls.
After an eventful election campaign, voting stations opened across France at 0600 GMT in 66,546 polling stations on Sunday for a high-stakes presidential run-off between centrist pro-EU Emmanuel Macron and far-right anti-immigration Marine Le Pen.
The run-off follows an unprecedented campaign marked by scandal, repeated surprises and a last-minute hacking attack on the front-runner Macron. Macron, the 39-year-old centrist emerged as the winner of the election's first round held last month.
The ex-economy minister wants to bridge the left-right divide, resisting an anti-establishment tide that has seen Britons vote to leave the EU and Americans choose Donald Trump as US president.
But should an upset occur and National Front candidate Marine Le Pen win, the very future of the EU could be on the line.
TRT World's Anelise Borges and Simon McGregor-Wood report from France.
Brief security scare
The courtyard outside the Louvre museum in Paris has reopened after a brief security scare prompted an evacuation of the site where French presidential candidate Emmanuel Macron plans to celebrate election night.
Explosives experts have left the site after a suspicious bag prompted the evacuation on Sunday of a few hundred people, primarily journalists preparing for Macron event. The museum itself was not evacuated or closed, and visitors continued entering and leaving.
Emmanuel Macron's campaign spokeswoman Pauline Calmes said that the courtyard outside the Louvre museum was evacuated because of a security alert, as a precaution.
The Louvre already was being heavily guarded after an attacker targeted soldiers near the museum during the presidential campaign.
Voter turnout in the run-off was above 65 percent late afternoon, a sharp drop of more than 6 percent compared to the last presidential vote.
The interior ministry announced Sunday the turnout had reached 65.3 percent, compared to 71.96 percent in the second round of presidential voting in 2012.
With many voters against both candidates and a high risk of abstention, a French baker is trying to knead out some support for the electoral system and is offering a free baguette to anyone who can prove they have voted.
"I did this for the regional elections in Calais, and hearing about the rumours in the polls of a record abstention for the second round of the presidential elections, I decided to do it again," Jean-Michel Coulon who runs the Le Fournil de la Tour bakery in Calais said. "To try and incite voters, on the small level that I could, to go and vote in the second round of the elections."
TRT World's Simon McGregor-Wood has more on the candidates voting.
Macron and Le Pen vote
French President Francois Hollande, Emmanuel Macron and Marine Le Pen have already cast their votes. Each candidate is expected to address their supporters later in the day.
Le Pen cast her ballot in Henin-Beaumont where her party won three years ago and controls the municipality - one of about a dozen the National Party and its affiliates runs.
Members of feminist group FEMEN protesters topless while wearing Putin masks protested outside the Henin-Beaumont polling station where and has been shoring up support. Some of the protesters were arrested by the police.
Macron voted in Le Touquet's city hall.
TRT World's Myriam Francois is in Paris with details of what to expect from both candidates on Sunday.
Most polling stations will close at 1700 GMT, except for those in big cities which will stay open an hour longer.
A first estimate of the results will be published at around 1800 GMT.
Macron campaign leaks
Hundreds of thousands of emails and documents stolen from the Macron campaign were dumped online on Friday hours before a campaign communication ban went into effect. The material was then spread by anti-secrecy group WikiLeaks.
The leak prompted the leading candidate to call it an attempt at "democratic destabilisation."
France's election authority said publishing the documents could be a criminal offence, a warning heeded by traditional media organisations but flouted by Macron's opponents and far-right activists online.
"We knew that there were these risks during the presidential campaign because it happened elsewhere. Nothing will go without a response," French President Francois Hollande said on Saturday.
There has been no claim of responsibility for the French hack, but the government and Macron's team previously accused the Kremlin of trying to meddle in the election – accusations denied in Moscow.
Big change for France
Whoever wins Sunday's vote it is set to cause a profound change in France, the world's sixth-biggest economy, a permanent member of the UN security council and a global military power.
It is the first time neither of the country's traditional parties has a candidate in the final round of the presidential election under the modern French republic, founded in 1958.
In case Macron wins the election, he would become France's youngest-ever leader.