He announced this on Sunday during midday prayers in St Peter's Square in front of tens of thousands of pilgrims.
He intends to canonise Piergiorgio Frassati (1901-1925) on 3 August next year in Rome, the Pope explained.
This Sunday will be the conclusion and highlight of a week-long worldwide youth meeting in Rome as part of the Holy Year.
Infected with polio
Frassati, the son of a wealthy liberal publicist and diplomat in Turin, was involved in helping the poor and marginalised as a student without his parents' knowledge and was a member of the Catholic People's Party, among others.
He died at the age of 24 as a result of poliomyelitis, presumably after contracting the disease while visiting a family suffering from polio.
Frassati has long been honoured as the patron saint of Catholic World Youth Days. He was beatified in 1990 by Pope John Paul II.
Pope Francis also wants to canonise Carlo Acutis (1991-2006), the Milanese youth known as the "cyber apostle", during the Holy Year. He recently announced the date for a Holy Year event for teenagers from 25 to 27 April.
With a canonisation by the Pope, the Catholic Church proclaims that a deceased person can rightly be venerated as a saint and called upon to intercede with God.
While saints are only venerated in a specific region, saints can be honoured by believers worldwide and invoked for intercession.