BL. PIERRE-JOSEPH CASSANT was born on 6 March 1878 in France to parents who were orchard-keepers as the second child born to them. He was a student at a boarding school run by De La Salle Brothers and it was here that his abilities in memorizing things were became quite diminished, leading to increasing learning difficulties. Despite these failings he was seen as a quiet and caring child.
It was at the age of 14 that he realized that he wanted to become a priest but his learning difficulties prevented him from entering the seminary. He went to the parish priest, Father Filhol, for advice. Father suggested he ask the Trappists, where Pierre-Joseph was accepted in 1894. He was placed under the charge of Father André Mallet who said to him: "only trust and I will help you to love Jesus".
During his novitiate he received the religious name of Marie-Joseph and was known for his strong determination to his studies to fulfill his lifelong wish of being ordained to the priesthood. He suffered from extreme tuberculosis around the time of his ordination and died not long after he was made a priest.
He often spent time meditating upon Christ in his Passion and on the Cross, depending on Him for strength during his studies. To further advance his chances of studying for the priesthood, he underwent further studies of the French language and began to learn Latin. It was around this time that he formed his personal motto, "all for Jesus, all through Mary".
He made his final vows on the Feast of the Ascension on 24 May 1900. From this point he focused on becoming a priest and he viewed Holy Orders in relation to the Eucharist as being a critical facet of the duties of a priest.The monk assigned to teach him humiliated and ridiculed him in public and said: "You are totally limited! It is useless for you to study. You will not learn any more. To ordain you would be a dishonor to the priesthood", yet Father Mallet assisted him with the course. His fellow seminarians thought well of him, and some said of him: "He was always happy. It's what made the beauty of his face".
Despite difficulties he was ordained as a priest on 12 October 1902. Immediately after this on 13 October, he was granted seven weeks of rest due to the advancement of tuberculosis he suffered. In spite of rest, his lungs were damaged beyond the point of repair, making his breathing difficult. His health continued to worsen when he returned to the monastery on 2 December 1902.In his illness it was Father Mallet who became his close aid and support. Bl. Pierre-Joseph said "when I can no longer say Mass, Jesus can take me from this world".
He became part of the Association of Victim Souls dedicated to the oblation of the Sacred Heart of Jesus Christ and signed an Act of Oblation to emulate the tenets of the organization. Bl. Pierre-Joseph followed in the footsteps Bl. Charles de Foucauld, SOG Alfredo Ildefonso Schuster, and Giuseppe Melchiorre Sarto, the future Pope Pius X.
Bl. Pierre-Joseph celebrated his final Mass on 31 May 1903 and received the last rites the following day.
He died in the dawn of 17 June 1903 after receiving Communion during a private Mass that Father Mallet celebrated for him; his final words were: "Jesus, Mary, Joseph, assist me in my last agony". Since his death there have been more than 2200 people from 30 countries that have reported miracles attributed to his intercession.
Pope (St.) John Paul II proclaimed him to be Venerable in 1984 and beatified him in 2004 after the approval of a miracle: the healing of a nine year old from cerebrospinal meningitis who was healed a day after praying to the future saint.