The teenager’s body, dressed in jeans and a pair of Nike trainers, lies in a glass-walled tomb in Assisi, visited by hundreds of thousands of people a year.
The canonisation of the so-called “cyber-apostle” was initially set for April but postponed when Pope Francis died. It will be US-born Pope Leo’s first such ceremony.
Among the crowds expected at the Vatican for the mass, which begins at 10:00 am (0800 GMT), are over 800 people travelling to Rome on a special train from Assisi.
The mass will also be watched by faithful on giant screens in Assisi, a medieval city and pilgrimage site in the central region of Umbria.
“I know that many will come, many will follow on television — many came already for April 27. And I’m sure that Carlo thanks them,” said his mother, Antonia Salzano.
In a video published by the Assisi diocese on Saturday, she said her son was proof that “we are all called to be saints… everyone is special”.
A large tapestry featuring a photograph of the saint-to-be hung on the facade of St. Peter’s Basilica ahead of the ceremony.
‘Exemplary life’
Acutis, born in London in 1991 to Italian parents, had an ardent faith, though his parents were not particularly devout.
He grew up in the northern city of Milan, where he attended mass daily and had a reputation for kindness to bullied children and homeless people, bringing the latter food and sleeping bags.
A fan of computer games, Acutis taught himself basic coding and used it to document miracles and other elements of the Catholic faith online.
Domenico Sorrentino, bishop of Assisi, called on young people on Friday to follow Acutis’s example.
“Today more than ever we need positive examples, exemplary life stories that can help our young people avoid following discouraging images, violent examples, and fleeting fads that leave nothing behind,” he said in a statement.
The Vatican has recognised Acutis as performing two miracles since his death — a necessary step on the path to sainthood.
The first was the healing of a Brazilian child suffering from a rare pancreatic malformation, the second the recovery of a Costa Rican student seriously injured in an accident.
In both cases, relatives had prayed for help from the teenager, who was beatified in 2020 by Pope Francis.
