The National Rally party on Sunday won a crushing victory in the first round of voting for the French National Assembly, bringing its long-taboo brand of nationalist and anti-immigrant politics to the threshold of power for the first time.

Official results published by the Interior Ministry showed that the party and its allies won about 33 percent of the vote, far ahead of President Emmanuel Macron’s centrist Renaissance party and its allies, which took about 20 percent to end in third place.

A coalition of left-wing parties, called the New Popular Front, won about 28 percent of the vote. Ranging from the moderate socialists to the far-left France Unbowed, the coalition was boosted by strong support among young people.

Turnout was high at about 67 percent, compared to 47.5 percent in the first round of the last parliamentary election in 2022, reflecting the importance accorded by voters to the snap election. To many it seemed that no less than the future of France was on the line with a far-right party long considered unelectable to high office because of its extreme views surging.

Over seventy candidates were elected outright on Sunday, but in most cases the election will be completed with a runoff on July 7 between the two or three leading parties in each constituency.

The results of the first round of voting do not typically provide a reliable projection of the number of parliamentary seats each party will secure. But the National Rally now looks very likely to be comfortably the largest force in the National Assembly, the lower house of Parliament where most power resides, although not necessarily with an absolute majority.

For Mr. Macron, now in his seventh year as president, the result of the vote was a severe setback after he gambled that the National Rally’s victory in the recent European Parliament election would not be repeated. There was no obligation to pitch France into summer turmoil with a rushed vote, but Mr. Macron was convinced that it was his democratic duty to test French sentiment in a national ballot.

The first round of voting suggested the most likely outcomes now are either an absolute majority for the National Rally or an ungovernable National Assembly. In the second scenario, there would be two big blocs to the right and left opposed to Mr. Macron, and his much-reduced centrist party would be squeezed between the extremes into relative powerlessness.

If the National Rally wins an absolute majority, it is expected to take the prime minister’s office and name cabinet members, limiting Mr. Macron’s powers, though he would remain as president.

Projections from several polling institutes suggested the National Rally would win between 240 and 310 seats in the runoff for the 577-seat National Assembly; the New Popular Front between 150 and 200 seats; and Mr. Macron’s Renaissance party and its allies between 70 and 120 seats. The ranges are broad because much can change in the week before the second round. For an absolute majority, a party needs 289 seats.

Mr. Macron, whose party and its allies have held about 250 seats since the last parliamentary vote in 2022, has been frustrated in his attempts to achieve his agenda by his lack of an absolute majority and inability to form stable coalitions. Now, with his seats likely slashed, the situation looks much worse for him.

In a statement immediately after the projections were released, Mr. Macron said that “confronted by the National Rally, it is time for a large, clearly democratic and republican alliance for the second round.”

Whether that is still possible at a moment when the National Rally has the wind in its sails is unclear.

Both leaders of the left and of Mr. Macron’s party said they would urge their candidates to pull out of some constituency races where they finished in third place in the first round. The goal is to avoid splitting the vote and to join in an effort to prevent the far right from winning an absolute majority.

“We must unite, we must vote for our democracy, we must prevent France from sinking,” said Raphaël Glucksmann, who led the center-left socialists in the European election.

In a statement of its own, Mr. Macron’s party declared: “We cannot give the keys of the country to the far right. Everything in their program, their values, their history, make of them an unacceptable threat against which we have to fight.”

Marine Le Pen, the leader of the National Rally, declared on Sunday night that France had voted “without ambiguity, turning a page on seven years of corrosive power.” She urged her supporters to ensure that her protégé, Jordan Bardella, 28, become the next prime minister.

Gabriel Attal, 34, once a Macron favorite and now almost certainly the outgoing prime minister after just six months in office, said that “if we want live up to the French destiny, it is our moral duty to prevent the worst from happening.” He noted that never in its history had the National Assembly run the risk of being dominated by the extreme right.

Mr. Macron’s decision to hold the election now, just weeks before the Paris Olympics, astonished many people in France, not least Mr. Attal, who was kept in the dark. That decision reflected a top-down style of governing that has left the president more isolated.

Mr. Macron was persuaded that a dissolution of the National Assembly and elections would have become inevitable by October, because his proposed deficit-cutting budget was expected to meet insuperable opposition.

“It was better to hold the election now,” said one official close to Mr. Macron who requested anonymity in line with French political protocol. “By October, an absolute majority for the National Rally was inevitable, according to our polling.”

Of course, the National Rally might end up with an absolute majority.

In the run-up to the election, Mr. Macron tried invoking every threatening specter, including a potential “civil war,” to warn people off voting for what he called “the extremes”: the National Rally with its view of immigrants as second-class and the far-left France Unbowed with its antisemitic outbursts.

He told pensioners they would be left penniless. He said the National Rally represented “the abandonment of all that forms the attractiveness of our country and retains investors.” He said the left would tax the vitality out of the French economy and shut down the nuclear power stations that provide about 70 percent of the country’s electricity.

“The extremes are the impoverishment of France,” Mr. Macron said.

But those appeals fell on deaf ears because, for all his accomplishments, including the slashing of unemployment, Mr. Macron had lost touch with the people to whom the National Rally appealed. Those people, across the country, said they felt talked down to by the president and that he did not understand their struggles.

Looking for a way to express their anger, they latched onto the party that said immigrants were the problem, despite an aging France’s need for them. They chose the party, the National Rally, whose leaders did not go to elite schools.

The rise of the National Rally has been steady and inexorable. Founded a little more than a half-century ago as the National Front by Ms. Le Pen’s father, Jean-Marie Le Pen, and by Pierre Bousquet, who was a member of a French division of the Waffen-SS during World War II, it faced for decades an ironclad barrier against its entry into government.

This was rooted in French shame. The collaborationist Vichy government during World War II deported more than 72,000 Jews to their deaths and France was determined that never again would it experiment with an extreme-right nationalist government.

Ms. Le Pen threw her father out of the party in 2015 after he insisted that the Nazi gas chambers were a “detail of history.” She renamed the party and embraced the smooth-talking and hard-to-ruffle Mr. Bardella as her protégé. She also dropped some of her most extreme positions, including a push for leaving the European Union.

It worked, even if certain tenets remained unchanged, including the party’s euro-skeptic nationalism and its determination to ensure that Muslim women be banned from wearing a head scarf in public. Also unchanged was its readiness to discriminate between foreign residents and French citizens, and its insistence that the country’s crime level and other ills stem from too many immigrants, a claim that some studies have challenged.

Mr. Macron, who is term limited and must leave office in 2027, appears to be facing a difficult three years ahead. Just how difficult will not be clear until the second round of voting is over.

How he would govern with a party that represents all he has resisted and deplored throughout his political career is unclear. If the National Rally gets the prime minister’s job, it will be in position to set much of the domestic agenda.

Mr. Macron has vowed not to resign in any circumstance, and the president in the Fifth Republic has generally exercised broad control over foreign and military policy. But the National Rally has already indicated it would want to limit Mr. Macron’s power. There is no doubt that the party will try if it gains an absolute majority.

By calling a snap election. Mr. Macron took an enormous, discretionary risk. “No to defeat. Yes to awakening, to a leap forward for the Republic!” he declared shortly after his decision was made. But as the second round of the election looms, the republic looks wounded, its divisions lacerating.