With a cottony ring of white hair and wearing a dinner jacket, rakishly unbuttoned white shirt, and no tie, Matthew Cvetic looks the part of an aging lounge singer. But the septuagenarian is sitting on a metal chair in the organ loft at St. Brigid’s Roman Catholic Church in Queens. He’s alone in his perch but is well aware of the Saturday evening Mass unfolding below. On an unseen cue, Mr. Cvetic walks to the bench at the organ and lays his fingers on the keys. Among the pews below, the faithful hear the music but rarely catch a glimpse of its player.

Every week, Mr. Cvetic – pianist, organist, singer, and voice coach – travels throughout all five boroughs by subway, inspiring hundreds of people as they baptize their children, bury their dead, or participate in weekly worship. In Spanish, Hebrew, Latin, or English, in churches, synagogues, and temples, Mr. Cvetic is there, working almost anonymously.

“How sweet!” Mr. Cvetic, 72, said on a recent Sunday, his voice as bright as a church bell. “I’m so glad you called. You want to interview me?”

The only hitch was that he didn’t know when he could squeeze in a meeting. On Sundays alone, he plays with the choir at the Madison Avenue Baptist Church’s morning Mass. At 3 p.m., he performs at the Catholic Church of the Good Shepherd. At 5:30 p.m., he plays the organ to accompany a solo singer for the evening worship service at Temple Emanu-El. And at 6:30 p.m., he gives voice lessons.

At the Church of the Good Shepherd, around the corner from the Lincoln Center, he plays piano and sings in Spanish for the members of the Iglesia del Espiritu Santo.

“My father’s Croatian,” he said. “My mother’s Slovenian.” But, he said he “knows more Spanish than Croatian,” which accounts for the ease with which he sings liturgical verse in the language. On a recent Sunday as the congregation lined up to take communion, Mr. Cvetic sang, “Hacia ti, morada Santa” or “Towards Our Heavenly Home.”

From there he usually catches the No. 67 bus heading east to Temple Emanu-El, where he pulls on a black choir gown and goes to the organ. He recites the evening prayer with the rabbi and the night’s singer. The rabbi reads a line and the woman sings. Mr. Cvetic responds with a flurry of earthy notes from the organ pipes.

Since he participates in Hebrew services, many are unaware of his Catholic upbringing. “Some places where I go, they say, ‘Are you Jewish?’ I hate that. What’s the difference if I’m Jewish?”

Mr. Cvetic shies away from speaking about his own faith. “Because of work, I’m involved in the church,” he says. “I don’t need to go to Mass. I used to go to the church and say my prayers.” Instead, he says he does “a Buddhist chant everyday.” As he hums his way through his day, it seems as though music is his only religion.

“It’s interesting how these different sects came out of the word,” he said. “It’s fundamentally the same. The word is designed to humanize the animal. Yet the animal takes the word and it becomes the weapon.”

Mr. Cvetic grew up in North Hills, a small town outside of Pittsburgh, Penn., where his mother was an organist at a local Catholic church. She began teaching him music when he was 7. By the time Mr. Cvetic was a teenager, he had become an organist for the St. Ambrose Church on the north side of Pittsburgh.

Around the same time, his father, also named Matthew Cvetic, abandoned the family for a life of stardom, booze, and casual lovers, according to the book “I Was a Communist for the FBI: The Unhappy Life and Times of Matt Cvetic,” by Daniel Leab. The senior Cvetic became a footnote in the history of the Cold War by selling a first person account to the Saturday Evening Post. In it, he described how he allegedly infiltrated the Communist Party in Pittsburgh for the FBI. The book tells a tamer tale: According to its author, Cvetic was a run-of-the-mill informant who knew how to play his cards. Either way, the article was serialized for radio and the story was ultimately made into a movie.

Mr. Cvetic was 14 when his parents divorced and rarely saw his father afterward.

He moved to New York City in 1964 after studying liturgical music at the University of Pittsburgh. He landed his first job at the now shuttered Bianca and Margarita’s in Greenwich Village, a restaurant that featured singing waiters, opera, and piano concerts. He continues to work restaurants. One Saturday night, after Mass at St. Brigid’s, he played Racine’s, an Italian eatery located at 108 East 38th St. He opened with a song from Giuseppe Verdi’s “La Traviata.”

In 1972, Mr. Cvetic’s fraternal twin brother, Richard, died suddenly of a heart attack. Mr. Cvetic said, “Jobs started falling apart,” after that. At St. Paul the Apostle Catholic Church, on the West Side, where he had been the organist for 20 years, he arrived so drunk that he couldn’t perform the ordination sermon. He missed a gig in Boston a week later, because he drank too much and forgot his schedule.

In the mid 1970s, he entered detox – he has been sober since September 1, 1976.

He said that being at church forces people to learn to be with each other in better ways as a community. Despite his personal aversion to organized religion, his professional affiliation with so may houses of worship gives him an appreciation for New Yorkers’ varying beliefs.

“There’s so much love in all the congregations I go to,” he said. And to him, music is central to bringing churchgoers together, whatever the language, whatever the song, whatever the melody. “If I have to raise the spirituality of people, I do it with the music at my disposal,” he said.