With the race exceptionally tight, it seemed an unlikely place for any candidate. Hardly a voter was in sight. Instead, what Mr. Macron later described as a “pilgrimage,” with some 20 journalists in tow, was in part intended to show his human side, to reflect his connection to a “terroir” — a definable place and personal history — that French voters could latch onto.

With no political party to speak of, and never having held elective office, Mr. Macron, 39, a onetime investment banker and former economy minister, is leading an improbable quest to become modern France’s youngest president. His profile is that of an insider, but his policies are those of an outsider. If the ever-precocious Mr. Macron is to succeed, his first challenge is to sell a product still largely unfamiliar to almost everyone: himself.

That Mr. Macron is such an unknown underscores his unusual position in a French election that, to some degree, is a referendum on the future of Europe. The far-right leader Marine Le Pen threatens to take France out of the European Union. By contrast, Mr. Macron is ardently pro-Europe and has portrayed himself almost as the anti-Le Pen.

The race is truly up in the air. As much as 30 percent of the French electorate is still undecided, and four of the 11 candidates, including Mr. Macron, are polling within three or four percentage points of each other. The top two vote-getters in the election’s first round will face off in a final vote on May 7.

Mr. Macron is so close to Ms. Le Pen, leader of the National Front, that it is difficult to say who is the front-runner. But Mr. Macron is buoyed by the fact that more than half of French voters support candidates other than those from the traditional, mainstream parties.

Mr. Macron has begun a new political movement, En Marche!, which means “Forward” or Onward,” that draws from both sides of the political spectrum. He is gambling that his postpartisan philosophy matches the national mood.

But the smartest kid in the class is not always the one who wins. Though he has already checked virtually every box required for a successful career among the French elite, Mr. Macron may actually be the kind of change agent France fears.

In a runoff — presuming both he and Ms. Le Pen get through to the final round — she would be the political placeholder, the vote to preserve or restore a nostalgic (critics say outmoded) vision of France and one that revives nationalism and fans anti-Muslim sentiments. She has expanded her movement by assailing globalization — the European Union, the loss of French jobs and an influx of migrants.

Mr. Macron is the establishment’s anti-establishment candidate. He tilts at sacred cows — retirement benefits, employee protections — with an eye toward making France more business-friendly, while professing he will preserve its social safety net. Many question whether he will really be able to do both at the same time.

Despite the political risks, Mr. Macron has proudly embraced an unpopular European Union, and preached tolerance toward immigrants and Muslims never beloved in France, and even less so since the 2015 terrorist attacks.

Yet he has clearly struck a chord with many voters, despite being “an unidentified political object,” as Pascal Perrineau, a political science professor at Sciences Po in Paris, described him.

“This is a man who, certainly, began his career in the Socialist Party, and he says that he is not a centrist,” Mr. Perrineau said. Yet, “he is, as he says, from the right and from the left and this is an invention that our political family has not seen before.”

The visit to Bagnères-de-Bigorre — almost four years to the day since Mr. Macron’s grandmother died — was a chance for the candidate to further define himself. At once sincere and strategic, the excursion was designed to portray him as someone with roots in the “real” France of villages and hard-working rural people.

“The journey I made today brought to mind many memories,” Mr. Macron later told a crowd of 5,000 at an evening rally nearby in Pau, a city of nearly 80,000, adding that it was where he used to reunite with his grandmother, “whom I loved so much.”

“It was she and my grandfather who for years and years led me to live in Bagnères-de-Bigorre, to walk there, to run there, to learn how to bicycle, to ski, to be rooted in our country,” he said.

Born and raised in Amiens, about 70 miles from Paris, Mr. Macron is the eldest of three children. Both parents are doctors. He attended a parochial school founded by Jesuits. When he was 15, he met Brigitte Trogneux, a teacher of French and drama with whom he fell in love. About 24 years his senior, she tried initially to discourage him, but he was determined and she was eventually smitten.

In a documentary broadcast on the France 3 television network, she recalled the year he went off to finish high school in Paris at the prestigious Lycée Henri IV. “He called me all the time,” she said. “We spent hours on the telephone. Little by little he conquered all my resistance in a manner that was incredible — with patience.”

She ultimately divorced her first husband and the father of her three children. One of them, a daughter, is working on Mr. Macron’s campaign. The student and his teacher married in 2007.

Their love affair was the kind of audacious undertaking that has defined Mr. Macron’s life and career. His sheer drive, his focus and his willingness to leapfrog in a country where most success is built step by step make him more like the entrepreneurs he admires than a typical politician.

A product of top schools, including the prestigious Sciences Po and the École Nationale d’Administration, Mr. Macron won a coveted place in an elite auditing body at the Finance Ministry before leaving to join the investment bank Rothschild & Company.

Although he knew little about investment banking, in four years at the firm Mr. Macron was promoted from director to managing director. He earned nearly 2.9 million euros ($3.1 million) in those years, according to the financial disclosure form from when he was economy minister.

By 2014, at 36, he was appointed minister of economy under France’s current Socialist president, François Hollande, before leaving to begin his campaign. His one significant achievement was passage of what became known as the Macron Law, a hodgepodge of economic policies mostly designed to cut red tape and make markets more flexible.

Those who have worked closely with Mr. Macron, both in government and in the private sector, are almost uniformly impressed by his grasp and dedication, but some said that at times they felt misled as Mr. Macron pursued his ambitions.