VATICAN CITY — The cardinals electing a new pope to lead the Catholic Church left the Sistine Chapel exhausted and hungry.

A meditation to start the conclave had dragged on and pushed their first vote deep into the evening. It had resulted in an inconclusive tally, with three main contenders. Keeping their vow of secrecy, they returned to Casa Santa Marta, the guesthouse where they were sequestered without their phones, and started talking.

Over dinner, as one gluten-free cardinal picked over vegetables and others shrugged at the simple fare, they weighed their choices. Cardinal Pietro Parolin, 70, the Italian who ran the Vatican under Pope Francis, had entered the conclave as a front-runner but hadn’t received overwhelming support in the vote. The Italians were divided, and some cardinals had become bothered by his failure to emphasize the collaborative meetings Francis prioritized for governing the church.

Cardinal Peter Erdo of Hungary, 72, backed by a coalition of conservatives that included some Africans, had no way to build momentum in an electorate widely appointed by Francis.

That left Cardinal Robert Francis Prevost, 69, a quiet American dark horse who had surprisingly emerged in the first evening’s vote as a source of particular interest.

A missionary turned religious order leader, turned Peruvian bishop, turned Vatican power player, he checked many of the boxes that a broad range of cardinals hoped to fill. His seeming ability to be from two places at once — North and South America — pleased cardinals on two continents. As the prelates sounded out the Latin American cardinals who knew him well, they liked what they heard.

At dinner, Prevost avoided any obvious politicking or machinations, cardinals said. By the next morning, he had become an unsuspecting juggernaut who left little room for rival candidacies and ideological camps.

“You begin to see the direction and say, ‘Oh my goodness, I’m not going to use my five days’ worth of clothes,’ ” joked Cardinal Pablo Virgilio Siongco David of the Philippines. “It’s going to be resolved very fast.”

Interviews with more than a dozen cardinals, who could divulge only so much because of secrecy rules that carry the penalty of excommunication, and accounts from Vatican insiders told the story of how Prevost became Pope Leo XIV. The swift, stunning and taboo-smashing consensus around an American unfamiliar to many outside the church came Thursday among an unwieldy College of Cardinals with many new members who didn’t know one another. They had different interests, languages and priorities, but a single choice.

After the death of Francis on April 21, cardinals from around the world began arriving in Rome. They joined powerful players in the Vatican who ran the church’s bureaucracy, including Prevost, whose career Francis had boosted.

Despite his intimate understanding of the Vatican, Prevost was still among the newbies, having been a cardinal not even for two years. And he had questions about the conclave.

He turned to one of the reported front-runners, Cardinal Luis Antonio Gokim Tagle of the Philippines, for help.

“How does this work?” the American said, according to Tagle, who recounted the conversation. “I had experience in a conclave,” Tagle said, “and he didn’t.”

Unlike Tagle, he also didn’t have the name recognition considered necessary in an election among so many new cardinals who barely knew one another. Without a high profile or obvious base of support, the Chicago-born Villanova University graduate moved below the radar.

“I didn’t even know his name,” David of the Philippines said.

But Prevost was not a complete unknown. As the former leader of the Order of St. Augustine, which operates around the world, and as the head of the Vatican office overseeing the world’s bishops, he had developed powerful connections and backers. First among them had been Francis, who put his career on the fast track. And his decades in Peru, fluent Spanish and leadership of the Pontifical Commission for Latin America gave him deep, and decisive, relationships on the continent.

“We almost all know him. He’s one of us,” said Cardinal Baltazar Enrique Porras Cardozo of Venezuela, who has known him for decades.

In the weeks before the conclave, the cardinals went to a series of private meetings to discuss their concerns about the future of the church. Unlike Francis, who made his mark with a short speech sharing his vision for the church, several cardinals said that Prevost’s remarks did not stand out. “Like everyone else,” said Cardinal Juan José Omella Omella of Spain.

Cardinal Jean-Paul Vesco of France, the archbishop of Algiers, also could not recall what the American had said, but he got to talk to him on the sidelines of the meetings — which was important, he said, because he was increasingly being talked about as a candidate based on his “incredible” resume, fluent Italian, reputation as a moderate and connection to Francis. The cardinal started asking around to people who had worked with the American to vet him and learned that he listened and worked well in groups. “I did my job,” Vesco said. “I have to vote. I have to know the person.”

Cardinal Wilton Gregory of the U.S. also said Prevost had engaged “quite effectively” in the smaller group discussions with cardinals.

Those more intimate settings played to Prevost’s strengths, as he had gained a reputation around Rome as a studiously prepared, collegial and organized collaborator, especially as a top Vatican department head.

“In the first vote, there were several candidates who won significant votes,” Cardinal Lazarus You Heung-sik of South Korea said, according to the news agency Yonhap.

The next morning’s votes — the second and third of the conclave — made the picture clear. “In the fourth vote, the ballots overwhelmingly shifted” to Prevost, You of South Korea said.

Later in the afternoon, they voted again, then counted the ballots one by one. When Prevost reached 89 votes, the two-thirds majority threshold needed to become pope, the room erupted in a standing ovation. “And he remained seated!” David said. “Somebody had to pull him up. We were all teary-eyed.”

As the counting continued and the votes for Prevost neared triple digits, Parolin had to ask them to sit down so they could finish.

“He obtained a very, very large majority of votes,” Cardinal Désiré Tsarahazana of Madagascar said.