Pope Leo was set to declare a 15-year-old computer whiz, Carlo Acutis, the first millennial saint on Sunday.
The move is thought to be designed to give the next generation of Catholics a relatable role model, who used technology to spread the faith and earned the nickname “God’s influencer”.
An open-air mass in St Peter’s Square in Vatican City – the first saint-making ceremony of Leo’s pontificate – was expected to draw hundreds of thousands of people and was also set to canonise another popular Italian figure who died young, Pier Giorgio Frassati.
Both ceremonies were scheduled for earlier this year, but were postponed following Pope Francis’s death in April.
Pope Leo is greeted by bishops in St Peter’s Square at the Vatican ahead of the service (Andrew Medichini/AP)
Francis had fervently pushed Carlo’s sainthood case forward, convinced that the church needed someone like him to attract young Catholics to the faith while addressing the promises and perils of the digital age.
Like Francis before him, Leo has expressed concern about the risks of technology, particularly artificial intelligence, and about online relationships replacing human ones.
Carlo was born on May 3 1991 in London to a wealthy but not particularly observant Catholic family. They moved back to Milan soon after he was born and he was said to have had a typical, happy childhood, albeit marked by increasingly intense religious devotion.
The youngster was particularly interested in computer science and devoured college-level books on programming even as a youngster.
The mother of Carlo Acutis, left to right, her children and husband (Domenico Stinellis/AP)
He earned the nickname “God’s Influencer”, thanks to his main tech legacy: a multilingual website documenting so-called Eucharistic miracles recognised by the church, a project he completed at a time when the development of such sites was the domain of professionals.
Carlo was known to spend hours in prayer before the Eucharist each day. The Catholic hierarchy has been trying to promote the practice of Eucharistic adoration because, according to polls, most Catholics do not believe Christ is physically present in the Eucharistic hosts.
In October 2006, at age 15, Carlo fell ill with what was quickly diagnosed as acute leukemia, and died within days. He was entombed in Assisi, which is known for its association with another popular saint, St Francis.
In the years since his death, young Catholics have flocked by the millions to Assisi, where they can see the young Carlo through a glass-sided tomb, dressed in jeans, trainers and a sweatshirt.
Carlo has proved to be enormously popular with young Catholics, who are said to see in him a relatable, modern-day role model.
Carlo Acutis’s childhood was marked by increasingly intense religious devotion (Domenico Stinellis/AP)
“It’s like I can maybe not be as great as Carlo may be, but I can be looking after him and be like, ‘What would Carlo do?’” said Leo Kowalsky, a secondary-school pupil at a school in Chicago, in the US, attached to the Blessed Carlo Acutis Parish.
The student said he was particularly excited that his own namesake — Pope Leo — would be canonising the patron of his school.
“It’s kind of all mashed up into one thing, so it is a joy to be a part of,” the pupil said in an interview last week.
Mr Frassati, the other saint being canonised on Sunday, lived from 1901-1925, when he died at age 24 of polio.
He was born into a prominent Turin family but is known for his devotion to serving the poor and carrying out acts of charity while spreading his faith to his friends.