John Román was born on March 6, 1546 in Carmona near Seville. He learned the merchant's trade in Seville. Then he returned to his hometown and opened a linen shop, but that work did not satisfy him. At the age of 19 he abandoned the business, gave his property away and became a hermit. From that moment on, he called himself John Grande Pecador (Great Sinner). However, life in seclusion was not his final vocation. He settled down in the city of Jerez de la Frontera where he took care of prisoners. In those times, prisons were more sites of torture and discomfort than rehabilitation centers, so prisoners needed everything, from food and clothes to medical care and simply humane treatment.

Due to his great commitment and good relationships with people leaving the prison, he was assigned supervision of a care facility for persons expelled from hospitals and shelters. He also helped women of the streets, gathering dowries for them so they would be able to start a family and abandon life in sin. He won the trust of a rich married couple who provided him with funds for opening a hospital in Jerez. Soon the facility became famous for good care of the sick and a deeply religious atmosphere.

In 1574 John Grande made an important decision. He affiliated his hospital with the Brothers Hospitallers of St. John of God and joined the order. The same year, during the plague epidemic, he organized help for its victims. The Archbishop of Seville ordered him to reorganize all the institutions taking care of the sick in the city.

He died on June 3, 1600 after contracting the plague. He was canonized by Pope John Paul II on June 6, 1996.