PARIS—Imane Laribi is like many young people in France: fresh out of school, struggling to start a career, and discontent with the choices before her in Sunday’s presidential election.

Facing a tough labor market, she and other young voters led the country’s revolt against its political establishment in the first-round of the election. Voters age 18 to 24 overwhelmingly supported candidates coming from outside France’s mainstream political parties: the far-left Jean-Luc Melenchon, Marine Le Pen of the far-right National Front and Emmanuel Macron, a centrist who founded his own party last year.

Ahead of Sunday’s final-round vote, polls show Mr. Macron consolidating the support of most young people behind him, garnering about 60% of the 18-to-24-year-old vote. That backing, however, masks deep skepticism among young people over his plans to address their most vexing challenge: landing a steady job.

Ms. Laribi, 22, doesn’t like Ms. Le Pen and her hard-edge stances against immigration and the European Union. But Ms. Laribi is uncomfortable casting a vote for Mr. Macron, the pro-Europe candidate, because she doesn’t trust his background as an investment banker at Rothschild & Cie.

“We all know the reputation of bankers,” said Ms. Laribi, a recent business-school graduate, “It’s complicated for young people now across France. I hope not, but I think he’s going to sink us.”

She voted for Mr. Melenchon in the first round, but with little enthusiasm. “I voted for him by default,” Ms. Laribi says.

Because people under 35 are less likely to go to the polls, their exact impact on Sunday’s vote is difficult to estimate.

Mr. Melenchon’s supporters are another wild card in Sunday’s runoff: 44% of them are expected to vote for Mr. Macron, 23% for Ms. Le Pen but 33% won’t say who they will pick, according to a poll this week by public opinion firm Elabe.

On the campaign trail, Mr. Macron has proposed relaxing France’s strict labor-market rules to fight unemployment. He has promised to go further than a meek overhaul passed last year—over violent youth protests while he was economy minister—that made it somewhat easier to hire and fire workers. His plans for an even deeper revamp are likely to face more resistance.

“I don’t understand how people can vote for him after that,” said Julien Breton, a 19-year-old who voted for Mr. Melenchon in the first round. “I think the laws should be changed, but not like that.”

Other young people say Mr. Macron’s free-market experience will make him a more effective reformer.

Clementine Dillard, a 24-year-old biology graduate student, cited Mr. Macron’s investment-banking career as a “strong point,” adding: “He perhaps know more about the economy than the others.”

The unemployment rate among people younger than 25 stands at 24%, up from 18% before the financial crisis in 2008. Across the Rhine, the German youth unemployment rate is just 7%.

Joblessness remains elevated for somewhat older French workers: The unemployment rate for those ages 25 to 29 is 14% compared with an overall rate of 10%.

Mr. Macron is seeking to address what many economists say is the main cause of the country’s youth unemployment. Its labor market is plagued by a sharp division between workers on indefinite contracts that contain strong legal protections against being fired and people on temporary contracts that last for as little as a few weeks.

If young people find work, it is increasingly through these temporary contracts. That makes it hard for them to qualify for loans or rent apartments.

“The integration of youth into the workforce has deteriorated over a number of years,” says Bruno Ducoudré, a labor-market economist at Sciences Po, a political-sciences university in Paris. “It’s taking longer and longer to find a nontemporary work contract.”

Mr. Macron has proposed a suite of measures to alleviate the problem, including financial penalties for businesses that hire too many workers on temporary contracts and new training programs to prepare young people for the workforce.

But economists caution that such programs will have only limited effects without stronger economic growth overall to create jobs for young and old.

“We finish our studies, and we know that it’s not easy to find a job, even if we have lots of degrees,” Ms. Laribi says, standing outside an employment office in the north of Paris. “I want to open my own company, but it’s really difficult.”

Ms. Le Pen has attracted a strong following among young people outside of France’s big urban centers, another sign of the sharp geographical divide that is shaping French politics. In Flixecourt, a town in France’s economically struggling north, French youth are voting overwhelmingly for Ms. Le Pen.

The message of leaving the EU, stopping immigration and imposing tariffs at the French border resonates strongly here. National Front, Ms. Le Pen’s party, argues that closing France’s borders would protect young and older workers from low-wage immigrant labor and manufacturers in Eastern Europe.

“We have to change the system,” said Romain Hemery, 25, “Strangers are coming to France, taking our work.”

Mr. Hemery, a carpenter, was let go from his job a few years and is now working for his father, who is also a carpenter.

“We have degrees and still nothing,” he says.