The Rev. Damien de Veuster's canonization date was set Saturday during a meeting between Benedict and cardinals at the Apostolic Palace.
De Veuster will be canonized along with four other people, the Vatican said.
In July, Benedict approved a miracle attributed to the priest's intercession, declaring that a Honolulu woman's recovery in 1999 from terminal lung cancer was the miracle needed for him to be made a saint.
He was beatified — a step toward sainthood — in 1995 by Pope John Paul II.
Born Joseph de Veuster in 1840, he took the name Damien and went to Hawaii in 1864 to join other missionaries of the Congregation of the Sacred Hearts of Jesus and Mary. Nine years later he began ministering to leprosy patients on the remote Kalaupapa peninsula of Molokai island, where some 8,000 people had been banished amid an epidemic in Hawaii in the 1850s.
The priest eventually contracted the disease, also known as Hansen's disease, and died in 1889 at age 49.
The Rev. Alfred Bell, who spearheaded Damien's canonization cause, said the priest had given his all to help those in need. "He went there (to Hawaii) knowing that he could never return," Bell told Vatican Radio. "He suffered a lot, but he stayed."
Bell said Damien's concern for others was a model for all the faithful today, particularly the young.
"Father Damien's example helps us to not forget those who are forgettable in the world," he said.
The Vatican's saint-making procedures require that a miracle attributed to the candidate's intercession be confirmed in order for him or her to be beatified. Damien de Veuster was beatified after the Vatican declared that the 1987 recovery of a nun of the Sacred Hearts of Jesus and Mary was a miracle. The nun recovered from an illness after praying to Damien.
After beatification, a second miracle is needed for sainthood.
The Vatican's Congregation for the Causes of Saints said Audrey Toguchi's 1999 recovery from lung cancer defied medical explanation, and in July, Benedict agreed. Toguchi, too, had prayed to Damien.
The Vatican announced the date for Damien's canonization and that of nine other people. Five will be declared saints at a ceremony April 26, five others, including Damien, on Oct. 11.