He had begun a thriving publishing venture both in Japan and in Poland in addition to his pastoral and spiritual work. These publications criticized the Nazis and marked him for imprisonment when the Nazis invaded Poland.
While he was interred in Auschwitz, he minister to his fellow prisoners and when ten randomly chosen prisoners were set apart for execution in retaliation for an escaped inmate, Kolbe volunteered to take the place of one of the victims.
For this and his life of holiness, he was canonized as a "Martyr of Charity," the first in the church's history so designated.
He is shown in a statue on Westminster Cathedral holding a book in which he points to the double crowns of purity and martyrdom which Our Lady had shown to him in a vision.