Bartholomew Mary Dal Monte was born in Bologna on 3 November 1726 to Orazio Dal Monte and Anna Maria Bassani. At the age of six and a half he received Confirmation from Cardinal Prospero Lambertini, Archbishop of Bologna, who was later to become Pope Benedict XIV. Even if the date of his First Communion is unknown, the boy's religious intentions have been preserved, which gave a Eucharistic dimension to his whole life.

A boy of lively intelligence and cheerful temperament, he received a thorough education in the humanities at the Jesuits' Santa Lucia College. But his priestly vocation encountered the bitter opposition of his father, who hoped that his son would be a banker. His missionary inclination was encouraged by a meeting with St Leonard of Port Maurice which confirmed the young man in his choice of the priesthood. He received priestly ordination on 20 December 1749.

The new priest was obliged to postpone his pastoral commitments for two years, since the Vicar General had asked him to complete his studies. He finished them brilliantly, earning a degree in theology. After spending his first years learning the art of preaching at the school of the most famous preachers of the time, Fr Bartholomew Mary began an extraordinary ministry of popular missions.

His activity was not limited to the parishes of Bologna: despite delicate health, he zealously spent all 26 years of his generous priestly life preaching in at least 62 Dioceses, in hundreds of popular missions, Lenten retreats and spiritual exercises for clergy, religious and lay people, working miraculous conversions and bringing about many reconciliations between contending parties. The "missions" became intensive workshops of religious instruction with systematic evangelization for all the faithful, at a time when the harmful consequences of certain ideas influenced by Jansenism and the Enlightenment were spreading.

He came to be known as "the missionary of discretion". His life was modeled on the ministry of Christ himself: intransigent in proclaiming the truth but welcoming and merciful to sinners. As a priest who belonged totally to God and was dedicated to the salvation of souls, he was a living image of the One who is "rich in mercy" (Eph 4:2), and was very devoted to Mary, Mother of Mercy.

Exhausted by his unremitting apostolic labours, during his last mission two months before he died, he prophetically exclaimed: "I am going to die in Bologna on Christmas Eve". On 24 December 1778 he serenely gave up his spirit, departing this life to celebrate Christmas in heaven. All Bologna mourned him deeply. Since 1808 his mortal remains have rested in the chapel of Our Lady of Peace in Bologna's Basilica of St Petronius.