MONTREAL — When the conductor ​​Yannick Nézet-Séguin was 10, he went to the basement of the family house, put on one of his parents’ vinyl records, held a yellow pencil aloft and began to conduct the first movement of Mozart’s Symphony No. 40, over and over again.

For the previous four years, the boy, obsessed by the rituals and pageantry of the Roman Catholic Church, had gone to the basement every day to conduct Mass by himself, earnestly telling his parents he wanted to become pope. So when he went upstairs to announce his new vocation, his mother and father, engaged in a game of after-dinner bridge, were ​amused.

“I was abnormally intense,” Mr. Nézet-Séguin, now 44, said with a laugh in between rehearsals at the Place des Arts concert hall in Montreal. “At that moment, my fascination with reli​g​ion was transferred to music and the liturgical aspect of the church became the ritual of the concert. My parents said, ‘Oh, whatever. In two weeks, you’ll want to become an astronaut.’ But I never changed my mind.”

Mr. Nézet-Séguin, who sometimes bleaches his short-cropped hair a vivid blond, has not disappointed his 10-year-old self. Last year, he became the third official music director in the history of the Metropolitan Opera in New York (“I expected his ‘Traviata’ to be good, but not this good,” wrote The Times’s chief classical music critic of the first opera that Mr. Nézet-Séguin conducted in his new post).