After completing his ecclesiastical studies, he taught theology and sacred eloquence and later was chosen Vicar-General of Bordeaux where he inaugurated a missionary movement.

[3] After preaching in the Diocese of Troyes the institute received from the Government of Emperor Napoleon I, unsolicited subsidies to defray the expenses of their missions.

They evangelized the French cities of Orléans, Poitiers, Tours, Rennes, Marseilles, Toulon, Paris and other places, and established the Works of St. Geneviève and the Association of the Ladies of Providence in many parts of France.

The royal family assisted him financially and gave him Mount Valerian, at that time the center of piety, and later one of the principal forts protecting the capital.

In 1839, at the suggestion of Bishop Hughes of New York, Forbin-Janson introduced the Fathers of Mercy into the United States, initially in the Diocese of New Orleans.

Ferdinand Bach, the first superior in America, became the Rector of the Cathedral of St. Louis in New Orleans where he died tending victims of yellow fever.

By a decree of Propaganda in August 1906, Theophile Wucher was named Vicar General of the Institute for three years and took up residence in New York.

The "Missionaries of Saint John the Baptist" is a Public Association of the Faithful recognized in the Roman Catholic Diocese of Covington.

It was founded by two former members of the Fathers of Mercy with the aim of establishing a new religious Institute of diocesan right which celebrates the liturgy according to the 1962 Roman Missal.