Above all he was molded by an extraordinarily fertile classical music world in his native province, Quebec. Time spent with him, his family and his friends in Montreal, where he lives, made clear the powerful influence of his roots and his long tie with the Orchestre Métropolitain, founded in 1981 for the sake of Québécois musicians. It is with that orchestra that he “puts on his slippers,” in the words of Lise Beauchamp, the orchestra’s principal oboist for 20 years. “Here we are like family,” she said.

Mr. Nézet-Séguin knows many of its members from their time at the conservatory together. His companion of 16 years, Pierre Tourville, is the assistant principal violist. One of his oldest and closest friends, Jennifer Bourdages, is the orchestra’s pianist.

It was also with the Orchestre Métropolitain that he plowed through the heart of the symphonic repertory: Mahler, Beethoven, Bruckner. By 26 he had conducted mammoth staples like Mahler’s Symphony No. 2 and Verdi’s Requiem. He and the orchestra have made 13 recordings. Mr. Nézet-Séguin is repeatedly asked, now that his career is on an international level, whether he will move. He always says no. “Do you want me to leave?” he once erupted when the orchestra’s board asked him the same question.

Quebec’s unusually rich classical music culture results partly from generous government spending on the arts and a strong Roman Catholic tradition that creates a heavy demand for church choirs and organists. The province, home to eight million people, has 12 orchestras, 7 conservatories (in addition to university music programs) and high classical music recording sales.

“We claim a lot here in Quebec that we are close to Europe and the French spirit,” Mr. Nézet-Séguin said. At the same time Quebecers are free of “this burden of generations of history,” he added. Two cultures and two languages create an “effervescence” as well as an “underlying energy that you always have to prove yourself, to make sure that you exist.”

“That’s very productive and very creative,” he said. Mr. Nézet-Séguin is part of a small wave of Québécois conductors on the international scene, including Bernard Labadie, founder of Les Violons du Roy in Quebec City; Jacques Lacombe, music director of the New Jersey Symphony Orchestra; and Jean-Marie Zeitouni, music director of the Columbus Symphony in Ohio.

“We are definitely currently in a golden era,” André Gremillet, managing director of the Melbourne Symphony Orchestra in Australia, said in an e-mail. Himself a Quebec native, Mr. Gremillet, while president and chief executive of the New Jersey Symphony, hired Mr. Lacombe as music director, starting in 2010.

It may seem odd that Quebec’s best-known conductor does not conduct Quebec’s top ensemble and one of Canada’s finest, the Montreal Symphony Orchestra. Rivalry with the Orchestre Métropolitain may be the reason. Mr. Nézet-Séguin made guest appearances early in his career, he said, but the last invitation came in 2004. He declined because of what he called a condescending tone.

“It’s not as if I need it,” he said, departing from his usual sense of diplomacy.

Madeleine Careau, the Montreal Symphony’s chief executive, said the orchestra invited him every year but, after repeated rejections, simply gave up. “Maybe he doesn’t want to conduct another Montreal orchestra,” she said. “We would love to have him.”

Returning to Montreal to work with the Orchestre Métropolitain remains a significant part of Mr. Nézet-Séguin’s life. In December he conducted each of two programs — the Bach-Bruckner pairing and Mahler’s Symphony No. 4 with a Bach cantata — at the Maison Symphonique and out in a neighborhood.

Mr. Nézet-Séguin was born the third of three children in 1975 in Montreal. His parents were university educators. He began piano lessons at 5, quickly absorbing repertory, and at 9 he joined the prominent Choeur Polyphonique de Montréal.

At 10 he announced his desire to conduct. “His playmates would pretend to play violin with a tree branch, and he would pretend to conduct with a stick,” said his mother, Claudine Nézet, now his personal assistant.

At 12 he started formal music studies at the Quebec Conservatory. He began leading the choir in rehearsals a year later and became its conductor at 18, as well as founding his own orchestra and choir, La Chapelle de Montréal.

Around then he wrote to his hero. As a boy Yannick haunted record stores and used his earnings as a church singer to vacuum up CDs. Having randomly picked up Brahms’s Symphony No. 1, conducted by Carlo Maria Giulini, he was smitten and bought many Giulini recordings.

“It was the clarity” of the music making, he said. “I felt I was hearing the score. Everything was in the right place. It transformed eventually my understanding of the spirituality of it or the humanity of it.”

Twice Mr. Nézet-Séguin wrote Giulini, a revered Italian maestro with the air of a musical high priest, asking to meet him. Finally, while in Trieste in the summer of 1997 for a four-hand piano competition, Mr. Nézet-Séguin was summoned to Milan for an audience with the maestro.

The two met a half-dozen times during Giulini’s last year of conducting. Mr. Nézet-Séguin traveled to sit in on rehearsals, attend concerts and go over scores with his mentor. Giulini never saw him conduct nor gave him an actual lesson in stick waving. But Mr. Nézet-Séguin said he learned important lessons.

“He was so respectful of everyone,” he said. “He had the capacity to make me feel more confident about my own ideas, which in the end is the best lesson in conducting. Any question I would ask him would always go back to: ‘How do I feel? How would I sing it? How do you keep things simple?’ ”

Mr. Nézet-Séguin counts two other individual influences: his piano teacher at the conservatory, Anisia Campos, a student of Alfred Cortot, and Joseph Flummerfelt, who runs weeklong conducting seminars in the summer at Westminster Choir College in Princeton, N.J. Mr. Nézet-Séguin attended two of them as a teenager.

Mr. Nézet-Séguin’s first major appointment arrived in 2000, when he became music director of the Orchestre Métropolitain. The circumstances were ugly, but he seems to have sidestepped any taint. His predecessor, Joseph Rescigno, a well liked conductor from New York, had invited Mr. Nézet-Séguin as a guest conductor. Abruptly the orchestra’s chairman and a former government minister, Jean-Pierre Goyer, announced that Mr. Rescigno would be replaced by Mr. Nézet-Séguin.

Mr. Rescigno later sued, saying he was forced out in violation of his contract, and won damages. In an interview Mr. Rescigno said he did not think Mr. Nézet-Séguin was aware of the machinations. Mr. Nézet-Séguin said his appointment “came as a total surprise.” (Mr. Goyer died in 2011.)

Another surprise, he said, was the music directorship of the Philadelphia Orchestra, which came 18 months after his debut with the orchestra, in December 2008, conducting Tchaikovsky’s Symphony No. 6. With perfect pitch he told the Philadelphia players at their first rehearsal that he had listened to Eugene Ormandy’s recording of the work with the Philadelphians over and over. It was the kind of reference to musical tradition that he often makes. “It felt from the first moment that we had known each other in a previous life,” Mr. Nézet-Séguin said.

The orchestra has been adrift, held together by the caretaker leadership of Charles Dutoit, for many years the music director of the Montreal Symphony. Philadelphia emerged from bankruptcy proceedings last year, the first major American orchestra to go that route.

Mr. Nézet-Séguin said his main goal in Philadelphia was “to grab the city again, to transform the pride the city has toward its orchestra to a much more proactive pride, a real passion for it, a sense of ownership.”

At that last Carnegie outing, the Verdi Requiem in October, Mr. Nézet-Séguin held his hand up for a good 20 seconds after the final chord expired before dropping his arms to his sides. He seemed stunned by the ovation.

Applause from his inner circle greeted him in the crowded dressing room. Attendants broke open bottles of sparkling wine. Mr. Nézet-Séguin embraced his companion, Mr. Tourville, looked him in the eyes and said, “Oui?”

“Oui,” Mr. Tourville answered.

With an air of coronation, orchestra and Carnegie Hall executives toasted Mr. Nézet-Séguin.

“It was my deepest wish that it would work here,” he said, “and it did.”