Early life
His father was German and his mother was Czech. He studied for the priesthood at Budweis seminary in south Bohemia and at Prague University. He spoke eight languages and was interested in botany and astronomy. When his ordination was delayed since his elderly bishop felt he had enough priests in Budweis, John sailed for New York. Here the bishop welcomed and ordained him and sent him to minister to German-speaking immigrants clearing forests near the Niagara Falls.

Joins the Redemptorists
Feeling isolated, John felt the need of a supporting community and joined the newly arrived Redemptorist community. After his novitiate he worked in Pittsburgh and Baltimore. Six years later he was made provincial of the Redemptorists in the US and in 1851 was named bishop of Philadelphia.

Pastoral work
Much of John's energy went into setting up schools and parishes for immigrants, building churches and visiting his diocese. He also wrote two catechisms and founded the School Sisters of Notre Dame, who as an active Franciscan Third Order staffed his schools and orphanages. He made the strenuous papal visits to Rome and was there in 1854 for the formal declaration of doctrine of the Immaculate Conception of the Blessed Virgin Mary.

Death
A small man, he spent much of his time encouraging nuns and lay people to live a hidden sanctity. Worn out by his labours, he collapsed one day on Vine Street, Philadelphia and died at the age of only forty-eight. In 1977 he became the first bishop from the United States to be canonised - by Pope Paul VI.