Local tradition maintains that Belley was evangelized in the 2nd century by the martyrs Marcellus and Valerian, companions of St.

[10] King Henry IV of France acquired the territory in which the diocese of Belley is located from Savoy in the Treaty of Lyon in 1601.

On 13 February 1790. it issued a decree which stated that the government would no longer recognize solemn religious vows taken by either men or women.

Members of either sex were free to leave their monasteries or convents if they wished, and could claim an appropriate pension by applying to the local municipal authority.

Penalties for refusing to swear the required oath were loss of income, deposition from office, arrest, trial, and deportation.

[22] Gabriel Cortois de Quincey, who had been the legitimate bishop of Belley since 1751, refused to take the oath, but before action could be taken against him, he died, on 14 January 1791.

[23] The electors of the department of Ain, not all of whom were Catholic, met at Bourg, and on 6 February elected as their constitutional bishop Jean Baptiste Royer, the parish priest of Chavannes-sur-Suran, some 20 km northeast of Bourg-en-Bresse.

He was consecrated, in a ceremony which was both schismatic and blasphemous, on 3 April 1791 in Paris at Nôtre-Dame, by Antoine-Adrien Lamourette, the constitutional bishop of Lyon.

To advance his aggressive military foreign policy, he decided to make peace with the Catholic Church and the Papacy.

In implementation of the concordat of 27 July 1817, between King Louis XVIII and Pope Pius VII, the diocese of Belley should have been restored by the bull "Commissa divinitus",[30] but the French Parliament refused to ratify the agreement.

It was not until 6 October 1822 that a revised version of the papal bull, now called "Paternae Charitatis" ,[31] fortified by an ordonnance of Louis XVIII of 13 January 1823, received the acceptance of all parties.

In the 17th century, it saw the foundation of the Joséphistes, a religious congregation founded by Jacques Crétenet (1606–67),[37] a layman and surgeon who became a priest after the death of his wife.

In 1858 the idea of a Trappist monastery in the Dombes district, which had been discussed for some years, was taken in hand by the newly appointed bishop, Pierre-Henri Gérault de Langalerie (1857–1871); Trappist monks finally occupied the still-unfinished monastery near the village of Le Plantay (45 km northewst of Lyon, on the road to Bourg) in October 1863.

[39] Cardinal Louis Aleman (1390–1450) was a native of the Diocese of Belley, [40] as was Sister Rosalie (1787–1856), noted in the history of modern Parisian charities.