John (or Giovanni) Leonardi was the youngest of seven children born in the Tuscan area of Lucca in 1541 to middle-class parents. At seventeen, he enrolled in pharmacy classes, studied hard for ten years, and earned his certification to work in the field. However, John had a lifelong interest in becoming a priest, and he quickly turned to the study of theology in order to get ready for ordination.

After being ordained in 1572, John quickly rose to the position of spiritual director for a select group of young men considering vocations as priests. They initiated the steps that would eventually result in the creation of the current Order of the Mother of God, also referred to as the Clerks Regular of the Mother of God, by setting up a communal way of living close to a local church.

Nonetheless, Lucca's civic authorities worked to prevent the establishment of a new religious order because they opposed it. Even though their efforts were eventually in vain, they made John Leonardi live outside of Lucca for the majority of the rest of his life, except for a few exceptional permits that the Pope's administration gave him.

John Leonardi and his order of priests aimed to increase the understanding and practice of the Catholic faith among both clergy and laypeople, in line with the spirit of the Catholic Counter-Reformation sparked by the Council of Trent. In a letter to Pope Paul V written at the beginning of the 17th century, he emphasized the general invitation to holiness of life for all members of the Church.

In 1595, John was entrusted to supervise the reform of two significant monasteries and secured papal sanction establishing the Order of the Mother of God. Even though the order's activities were mostly restricted to Italy, John founded a college for overseas missionaries in response to advice from his spiritual mentor, St. Philip Neri. This seminary is now known as the College for the Propagation of the Faith.

On October 9, 1609, St. John Leonardi passed away in Rome after becoming ill and dying while tending to plague victims. In 1938, Pope Pius XI canonized him. As a result of his initial professional path, he was named the patron of pharmacists in 2006. His feast day is celebrated on October 9.

Other Saints of the Day
St. Alfanus
St. Benito de Jesus
St. Domninus of Fidenza
St. Victoriano Pio
St. John Henry Newman