The Guardian once observed that for millions of Britons and millions more BBC radio listeners around the world, Christmas did not begin until afternoon turned to evening on Christmas Eve, and a single boy treble from the choir of King’s College at Cambridge stepped forward to sing the first words of the first carol in an annual musical tradition that dated to 1918:

Once in royal David’s city

Stood a lowly cattle shed,

Where a mother laid her baby

In a manger for his bed:

Mary was that mother mild,

Jesus Christ her little child.

For the past 37 years, that service from the magnificent vaulted King’s College Chapel, the Festival of Nine Lessons and Carols, was led by Stephen Cleobury, who as director of music at King’s College presided over one of the most acclaimed liturgical choirs in the world.

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Founded in the 15th century by King Henry VI, the choir served primarily to provide music for the chapel’s daily religious services. But through concerts, international tours and the Christmas Eve service, which was said to reach 100 million radio listeners in a given year, the all-male choir developed a reputation that extended far beyond Cambridge, Britain and even Europe.

Mr. Cleobury, who was credited with safeguarding the traditions and quality of the choir while also helping to lead choral music into the future by commissioning new works from contemporary composers, died Nov. 22 in York, England. He was 70. The cause was cancer, according to his U.S. manager, Janet Jarriel.

Known for their longevity in their post, past choirmasters at King’s College have outlasted British monarchs. Mr. Cleobury, an accomplished organist who previously had played for the royal family during services at Westminster Abbey in London, followed Philip Ledger and before him David Willcocks when he assumed the role in 1982. Shortly before his retirement in September, Mr. Cleobury was knighted by Queen Elizabeth II.

Mr. Cleobury was known for the self-effacing approach he took as he led the 16 boy choristers and 14 older choral scholars in his ensemble, all of them, Mr. Cleobury included, clad in red cassocks and white surplices. At the Christmas Eve service, the boys did not know who would sing the opening solo until moments before the BBC began broadcasting and Mr. Cleobury called the soloist forward. He did not wish for the pressure to weigh on the boy any longer than necessary, he said.

“He was not a showman, and he was not egoistical,” said Michael McCarthy, director of music at Washington National Cathedral, where the King’s choir regularly performed over the years. “He had high standards, but it was not about him,” McCarthy continued, describing Mr. Cleobury’s skill in creating a choir that was “molded to sing like one.”

Some of his young singers would pursue musical careers; others would not. At auditions he looked not for impeccable musical preparation, he told the Observer, but rather a “sparkle in the eye” and a simple love of music. The Daily Telegraph once described his choristers admiringly as “13 going on 65.”

Mr. Cleobury was especially known for the new compositions that he featured alongside the sacred standards at the Christmas Eve service, which retold the story of the Nativity through music. Of the works he commissioned, Mr. Cleobury said his favorites were John Rutter’s “What Sweeter Music” and Judith Weir’s “Illuminare, Jerusalem.” Other composers he tapped included John Tavener, Arvo Part and Harrison Birtwistle.

The modern works were not always met with favor. Once, a listener wrote to Mr. Cleobury saying that “whoever commissioned that carol should be locked in a darked room and never let out.” But he stood firm in his conviction that new compositions kept the choir — and choral music — vital into the modern era.

“For me, it has been a minor crusade,” he told the classical music website Bachtrack. “I happen to think that quite a lot of music that’s written nowadays for the church is not of very high quality. I don’t think that the church needs to put up with mediocre music.”

Mr. Cleobury was ever cognizant of not only the music he selected for his young singers but also the venue in which they performed. King’s College Chapel, a late-Gothic structure with soaring stained-glass windows, was both an architectural marvel and a bedeviling acoustical challenge.

“If you made a bad sound you’d have to suffer it for six seconds,” a baritone, Gerald Finley, once told the New York Times. “One geeky choral scholar calculated that if you made a mistake on Christmas Eve, the combined number of people listening on radio with the chapel echo would be like one person hearing that mistake continuously for 24 years.”

Stephen John Cleobury was born in Bromley, England, on Dec. 31, 1948. His father was a physician who often played the church organ, and his mother was a nurse and secretary of a local music festival, according to the Times of London. The family lived for a period in a mental hospital when his father trained as a psychiatrist.

Mr. Cleobury studied the piano and was a chorister at Worcester Cathedral before becoming an organ scholar at St. John’s College at Cambridge, where he studied under choral conductor George Guest. Before his appointment at King’s College, he was master of music of Westminster Cathedral, a rare appointment for an Anglican at the Catholic church.

At King’s, he started King’s Voices, a mixed-voice ensemble that allowed female and male students to sing in the storied chapel. He recorded extensively with the choir and also cultivated what Gramophone described as “an impressive recorded legacy of his own across a wide breadth of repertoire, from the early music of Byrd and Purcell through to the core works of the 20th century Anglican tradition and the composers of our own day — even recording solo recitals on King’s magnificent organ.”

His first marriage, to Penny Holloway, ended in divorce. In 2004, he married Emma Disley Hebblethwaite. In addition to his wife, survivors include two daughters from his first marriage, Suzannah and Laura; two daughters from his second marriage, Olivia and Frances; a stepdaughter, Alexandra; a sister; a brother; and six grandchildren.

In addition to his post at King’s College, Mr. Cleobury served for many years as conductor of the BBC Singers and the Cambridge University Musical Society. Last year’s Festival of Nine Lessons and Carols, his final, coincided with the centennial of the event. For many Britons who no longer attend church services, it is an abiding sacred element of the Christmas season.

“It’s very important that we do the right thing by people of genuine Christian conviction, but it’s also important that we welcome and include people who have different views, including those who have lost all faith or who come from different faiths,” Mr. Cleobury told the Guardian.

“We are providing something that people can connect with in different ways,” he said. “Hearing ‘Once in Royal David’s City’ or ‘In the Bleak Midwinter’ connects people with something earlier in their life and provides a solace of some kind.”