Emmanuel Macron won by a larger margin than expected, 58.55 percent to 41.45 percent.
At the foot of the Eiffel Tower, the centrist leader told jubilant supporters that now that the election was over, he would be a “president for all.”
He is the first sitting president to be re-elected in 20 years.
Despite her defeat, Ms Le Pen, 53, declared that her large vote share was still a victory.
In 2011, Marine Le Pen took over the party founded by her father, Jean-Marie Le Pen, in an attempt to make it electable. On Sunday, she received more than 13 million votes on a platform of tax cuts to combat rising living costs, a ban on wearing the Muslim headscarf in public, and a referendum on immigration controls.
More than one-third of those who voted did not vote for either candidate. Turnout was just under 72%, the lowest in a presidential run-off since 1969, and over three million people voted spoilt or blank.
The day of the election, much of France was on vacation, but the low turnout also reflected the apathy of voters who complained that neither candidate represented them. Voters who said they were voting with blank ballots told the BBC that they were doing so to punish the current president.
Anti-Macron protesters took to the streets in a number of cities, including Paris, Rennes, Toulouse, and Nantes, refusing to accept the outcome.