Born in London in 1991 to Italian parents, he lived his life in Milan. He died of leukemia in 2006, 15 years old.
About 80,000 spectators, many young, were in the crowd during Sunday's ceremony in the Vatican.
Carlo Acutis liked to play computer games, learned to program himself and used the internet to spread his Christian faith. As a modern saint, he has been called both "God's influencer" and "cyberapostle".
His mother, Antonia Salzano, said that her son is proof that "we are all called to be saints, everyone is special".
Canonization is preceded by a long and complicated process, where the Catholic Church in different stages and ultimately the Vatican investigates the person in question. Two miracles are required.
The first miracle attributed to Carlo Acutis was the healing of a Brazilian boy who suffered from a rare defect in the pancreas.
The second was the recovery of a Costa Rican student who was seriously injured in an accident.
In both cases, relatives had asked for help from the teenager, who was beatified in 2020 by Pope Francis.
Carlo Acutis' preserved body rests in a grave with glass walls in the city of Assisi in Italy, dressed in jeans and a pair of Nike shoes. Almost a million pilgrims visited the grave last year.
Pier Giorgio Frassati, an Italian mountaineer and engineering student, who died of polio at the age of 24 in 1925, was also canonized on Sunday.
