PARIS — President Emmanuel Macron of France won a crucial stamp of approval on Sunday as voters gave him and his allies a decisive majority in parliamentary elections, but a record-low turnout cast a shadow over his victory, pointing to the hurdles he will face as he seeks to revive the country’s economy and confidence.

When the votes were counted, Mr. Macron’s party, La République en Marche (the Republic on the Move) and its allies had won 350 seats in the 577-member National Assembly, the lower house of Parliament.

Mr. Macron, a relative political newcomer who was elected on May 7, had called for a strong mandate to advance his legislative agenda, including plans to loosen France’s restrictive labor laws. Voters swept in many first-time candidates, including some of Arab or African ancestry, and elected more than 200 women, a record in France’s modern history.

For the two mainstream parties, the outcome was a bleak repudiation: The center-right Republicans and their allies were relegated to a distant second place, with an estimated 135 members for its bloc in Parliament, while the Socialists and their allies, who had a majority in the last election, saw their bloc reduced to an estimated 45 seats.

The former Socialist prime minister Manuel Valls appeared to have barely won re-election in his district, by a margin of just 139 votes. His opponent made accusations of improprieties and asked for a recount. Several prominent Socialist representatives, including four who served as ministers in the previous government, lost their seats.

Parties on both the far left and the far right won more seats — and Mr. Macron’s bloc won fewer — than analysts had projected in the past week. Still, Mr. Macron “has all the powers,” said Jean-Christophe Cambadélis, who resigned on Sunday as head of the Socialist Party, which with its allies won both the presidential and the parliamentary elections of 2012, only to see their popularity erode under the leadership of Mr. Macron’s predecessor, François Hollande.

A top Republican official, François Baroin, wished Mr. Macron “good luck” but said his party would continue to be heard, as the largest opposition party. Most of the better-known Republicans were re-elected, but Nathalie Kosciusko-Morizet, a moderate and one the party’s top officials, lost to a Macron-backed candidate in her Paris district.

The record-low turnout, about 43 percent, dimmed Mr. Macron’s victory and pointed to the tentative, even ambivalent, view of many French citizens toward his promises to transform France.

“Many people are in a state of uncertainty, a ‘wait and see,’” said Luc Rouban, a professor at the Center for the Study of French Political Life at Sciences Po.

“The level of abstention in the second round is a sign that a large part of the working-class electorate are not going to vote anymore,” Mr. Rouban said, describing the sense of alienation evident in the abstention as “an invisible fracture” separating the poorest and more modestly off members of French society from the rest.

Mr. Macron’s opponents seized on the abstention rate to try to discredit his victory. The leader of the far-left France Unbowed party, Jean-Luc Mélenchon, said the abstention level was “crushing,” adding, “Our people have entered into a form of civic general strike.” He suggested that with such a high number of people declining to vote, the government was robbed of its legitimacy.

A majority of eligible voters did not show up, perhaps because they thought Mr. Macron’s candidates did not need their support or, more worryingly for Mr. Macron, because they were unwilling to give him their endorsement. Many might have been tired of voting, having been called to the polls not only for the two rounds of the presidential election and then two rounds of voting for Parliament, but also for primary elections on the left and the right ahead of the presidential election.

Nonetheless, the overall picture for Mr. Macron was a positive one.

“A year ago, no one could have imagined such a political renewal,” Prime Minister Édouard Philippe said, adding: “Abstention is never good news for democracy. The government interprets it as a strong obligation to succeed.”

Mr. Macron, 39, has seemed like a golden child of Western liberal democracy of late, with his stunning rise to power in little more than a year and his seemingly unerring sense of how to exercise it in his first weeks in office.

But Sunday’s abstention rate suggests that he has yet to convince many French voters that his ideas and legislative program will make their lives better. The high rate could spur union-led street protests, a longtime staple of French politics, especially if Mr. Macron tries, as he has promised, to fast-track part of his legislative program.

Still, with 350 representatives elected on the ballot of La République en Marche or its close ally, the Democratic Movement, Mr. Macron could justifiably say that a majority of those who voted chose his program of loosening France’s restrictive labor laws, making it easier for businesses to hire and fire employees, and reducing worker protections with the goal of creating more jobs.

The National Assembly, France’s lower and more powerful house of Parliament, will lose little time getting to work and — if all unfolds as Mr. Macron hopes — the steps will begin to change France. Although Parliament will not vote on key measures in its first few weeks in office, it will start discussing the measures later this summer, setting the stage for rapid passage in the early fall, including the contentious overhaul of France’s labor laws.

Also on tap for completion in the next four months is a potentially controversial codification in common law of some measures in the current state of emergency, such as the ability to conduct house raids or place people under house arrest without the prior authorization of a judge. An ethics law for politicians is also expected.

In Sunday’s voting, Marine Le Pen’s far-right National Front party and its allies saw a precipitous drop in support since the presidential election, winning nine seats. Ms. Le Pen herself won her race for a seat in a district of northern France, but the No. 2 in her party, Florian Philippot, lost his race. Just two months ago in the immediate aftermath of the first round of the presidential election, analysts had predicted that the National Front might obtain more than 50 seats.

Mr. Mélenchon, the far-left leader, won his seat in a district in the Mediterranean port city of Marseille. His party and its Communist allies won 27 seats, fewer than might have been expected after Mr. Mélenchon’s strong showing in the presidential election, but enough to challenge the Socialists for the status as the main left-wing opposition party.

Only the mainstream right party, the Republicans, and its allies managed to maintain a significant presence in Parliament.