Opinion polls show centrist Emmanuel Macron easily winning the final clash against 48-year-old Marine Le Pen after he qualified for the May 7 run-off.
Sunday's outcome saw Macron leading the ballot with 23.75 percent of the votes, slightly ahead of Le Pen who was at 21.53 percent, according to final results. Voter turnout for the first round was 69.42 percent of around 47 million people eligible to cast their ballots.
Macron drew immediate support from his defeated rivals from the Socialists and Republicans. He started his own party, En Marche, a year ago and has never participated in parliamentary elections.
Socialist Benoit Hamon, who won a humiliating 6.35 percent, said the left had suffered a "historic drubbing" but urged voters to keep out Le Pen whom he called "an enemy of the republic."
Scandal-hit Republican candidate Francois Fillon followed suit, saying: "There is no other choice than voting against the far-right."
Le Pen's father, Jean-Marie Le Pen, who founded the National Front in the 70s, lost the presidential race to Republican Jaques Chirac in 2002.
Le Pen says Macron weak on terrorism
Le Pen on Monday launched a scathing attack against Macron, calling him "weak" in the face of the terror threat.
"I'm on the ground to meet the French people to draw their attention to important subjects, including Islamist terrorism to which the least we can say Mr Macron is weak on," Le Pen told reporters.
"Mr Macron has no project to protect the French people in the face of Islamist dangers," she said, adding that the run-off with Macron was a referendum on "uncontrolled globalisation"."
The euro surged after Macron won the round. Investors globally had been watching the vote fearing that a wave of populism – which swept Donald Trump to the White House and saw Britain leave the EU – could lead to a win for the anti-European Le Pen and put the future of the bloc in doubt.
Traders gave a huge thumbs-up, sending the euro flying above $1.09 at one point before paring the gains to $1.0846 from $1.0726 in New York on Friday.
"Given that pre-vote polling shows that Macron should trounce Le Pen on May 7, markets are already celebrating as though Macron is already the president of The Republic," Greg McKenna, chief market strategist at AxiTrader, said in a note.
"President of patriots"
With an eye to Le Pen's avowedly France-first policies, Macron told the crowd: "I want to be the president of patriots in the face of a threat from nationalists."
If he wins, Macron's biggest challenges will lie ahead, as he first tries to secure a working parliamentary majority for his young party in June. He will then need to seek broad popular support for labour reforms that are sure to meet resistance.
Le Pen, who is herself bidding to make history as France's first female president, has done much to soften her party's image. The leader of the National Front found widespread support among young voters by pitching herself as an anti-establishment defender of French workers and French interests against global corporations and an economically constricting EU.