But the survey found that neither the Front National nor En Marche ! would win an absolute majority in Parliament.
Macron said Le Pen was a "high priestess of fear" who would start a civil war, while Le Pen said her rival was a "darling of the elite."
The party deputy said a controversial speech was a deliberate "nod" to one given by rival François Fillon.
The French far-right leader's extreme Euroskepticism would pose an existential threat to the bloc.
Polls predict Macron, a former economy minister, will win the May 7 run-off with about 59-60 percent. But the momentum has recently been with Le Pen, who has clawed back about five percentage points over the past week.
Earlier this year, Le Pen repeatedly said that, if elected, she would seek a radical loosening of the EU's structure and, within six months, call a referendum on the outcome recommending a 'Frexit' divorce.
Le Pen said she and Nicolas Dupont-Aignan shared a "common project that we will promote together."
Since taking over the leadership in 2011, Le Pen has sought to soften her party's far-right image, but for many voters the association remains.
Marine Le Pen faces a huge uphill battle to defeat Emmanuel Macron in the second round of the French election.
After Francois Fillon's demise and Emmanuel Macron's rise, the Russian establishment looks to Marine Le Pen.
Expatriates in seven African countries overwhelmingly backed centrist newcomer Macron, while the far-right Le Pen fared badly.
The euro currency rose to its highest point since mid-November after Macron was revealed as the winner.
Here's what to make of the results from one of Europe's most exciting contests, as it heads into its second round on May 7.
The election now heads into its second round, set for May 7.
Final results are expected before midnight local time.
With two anti-globalization candidates whose policies could break up the EU among the four front-runners, the vote is of major significance to the international political status quo.
Le Pen is way down in the polls. But her base is energized, and as the French economy sputtersr and fears of Islamist militants grow, it may be too soon to discount her chances.
The contest's first round has become a tight four-horse race, and trusting the polls is a risky business.
The 2017 French presidential election is probably going to be Europe's most important this year.