PARIS — In a serious blow to President Emmanuel Macron of France, his centrist coalition was projected to lose its strong majority in the lower house of Parliament on Sunday, after crucial elections that saw the far-right and an alliance of left-wing parties surge in seat numbers, leaving him with a slim lead and complicating his second term.
Projections based on preliminary vote counts gave Mr. Macron’s centrist coalition 205 to 250 seats in the 577-seat National Assembly, the lower and more powerful house of Parliament — more than any other political group, but less than half of all seats.
For the first time in 20 years, a newly elected president appeared to have failed to muster an absolute majority in the National Assembly, which will not grind Mr. Macron’s domestic agenda to a halt, but will shift power back to Parliament after a first term during which Mr. Macron’s top-down style of governing had mostly marginalized lawmakers.
The results were a rebuke of Mr. Macron who appeared disengaged in the campaign and more preoccupied by France’s diplomatic efforts to support Ukraine in its war against Russia. Speaking on an airport tarmac before a trip to Eastern Europe that took him to Kyiv, the Ukrainian capital, this past week, he had urged voters to give him a “solid majority” for the “superior interest of the nation,” but he did little campaigning himself.
“It’s not the result we were hoping for,” Gabriel Attal, Mr. Macron’s budget minister, told the TF1 television channel on Sunday, as he acknowledged that his party and its allies would have “to find a stability” in Parliament if they wanted to push through legislation.
Mr. Macron’s recently nominated prime minister, Élisabeth Borne, was projected to win her race, as was Gérald Darmanin, his tough-talking interior minister. But several of his key allies appeared to have lost, including Richard Ferrand, the president of the National Assembly, and Amélie de Montchalin, his minister for green transition — a stinging rebuke for the president, who had vowed that cabinet ministers who failed to win a seat would have to resign.
The alliance of left-wing parties, known as the Nouvelle Union Populaire Écologique et Sociale, or NUPES, and led by the leftist veteran Jean-Luc Mélenchon, was expected to win 150 to 190 seats. The alliance includes France Unbowed, Mr. Mélenchon’s party, as well as the Socialists, Greens and Communists.
That was not enough to seize control of the National Assembly and force Mr. Macron to appoint Mr. Mélenchon prime minister, as the leftist coalition had hoped. But it was a strong showing for parties that had been largely written off as hopelessly divided. Much of the campaign was a bruising confrontation between the leftist coalition and Mr. Macron’s forces, with both sides describing a potential victory by their opponents as an unmitigated catastrophe.
Mr. Mélenchon, in a speech on Sunday to cheering supporters in Paris, called the results “absolutely amazing.”
“The presidential party’s defeat is complete,” he said. “We reached the political objective that we had set for ourselves.”
The alliance he brought together will be the main opposition force in the National Assembly, but major policy differences among coalition members on issues like the European Union could resurface once Parliament is in session later this month.
In 2017, when Mr. Macron was elected for the first time, his party and its allies clinched a commanding majority of 350 seats in the lower house of Parliament, which was mostly compliant with his plans.
This time, with a far slimmer majority and a much stronger opposition on the left and on the far-right, Mr. Macron’s centrist coalition, known as Ensemble, could struggle to pass certain bills, potentially forcing him to reach across the aisle to opposing lawmakers to secure a bill’s passage.
“The way the president will be able to govern through his prime minister is rather uncertain at the moment,” said Étienne Ollion, a sociologist and professor at the Polytechnique engineering school.
It was not immediately clear what other allies Mr. Macron’s coalition might find in Parliament to form a working majority, although Mr. Ollion said the most likely fit would be the center-right Les Républicains party, which was projected to win 60 to 80 seats. Mr. Macron will be much more dependent on his centrist allies than he was during his first term, especially to pass contentious projects like his plan to raise the legal age of retirement to 65 from 62.
The vote was also marred on Sunday by record-low turnout, a warning sign for Mr. Macron, who has promised to rule closer to the people for his second term. Only about 46 percent of the French electorate went to the ballot box, according to projections, the second-lowest level since 1958.
The National Rally, the party of the far-right leader Marine Le Pen, was projected to secure 75 to 100 seats in the National Assembly, far more than was expected after she was convincingly defeated by Mr. Macron in the presidential election in April and then ran a lackluster campaign for the parliamentary one.
That would make it the third biggest political force in the lower house and a much stronger force than the handful of lawmakers it had until now. Ms. Le Pen herself was handily re-elected to her seat in a district in northern France.
“This group will be by far the largest in the history of our political family,” Ms. Le Pen said in a speech on Sunday, promising her supporters that she would defend the party’s hard line on immigration and security.