Traditionally, it formed part of Lower Brittany; today's diocese is coextensive with the Department of Finistère.

Nothing accurate is known about him, but he is supposed by some to have been ordained by St. Martin of Tours in the fourth century, while others claim that he was a sixth-century monk.

460–532), the alleged first Abbot of Landevennec, is, as Robert Latouche has shown, devoid of historical merit, and the documents on which it depends complete forgeries.

[7] There is evidence that Christianity was preached in Léon twenty years before the evangelization of Cornouaille, but ancient Breton chronology is very uncertain.

The legend of St. Paul Aurelian, written in 884, shows that the Breton monks believed the See of Léon had been founded in the Merovingian epoch.

Paul Aurelian, a Gallic monk, founder of monasteries at Ouessant on the north-west coast of Brittany and on the Island of Batz, was believed to have founded in an abandoned fort a monastery which gave origin to the town of St. Pol de Léon, afterwards the seat of a diocese.

He was the first titular of the see, a wonder-worker and prophet, and was held to have died in 575 at the age of 140 years, after having been assisted in his labours by three successive coadjutors.

When Alexander VI granted that church the same indulgences as could be gained at the Roman Jubilee, funds came in which allowed its completion.

[11] The Church of Notre Dame de Creisker, in the same town, restored in the fourteenth century, has a belfry which the Bretons claim to be the handsomest in the world.

Along with all abbeys, convents, and monasteries, it was suppressed by the National Constituent Assembly and by the Civil Constitution of the Clergy.

"Apostle of Brittany" Father Julian Maunoir worked as a missionary to the Breton people for 43 years.

The Jesuits were established in the Collège de Quimper in 1620 where they flourished until the Society of Jesus was expelled from France in 1763.

[12] Other notable persons whose origins were in the Diocese of Quimper are: the classical scholar Jean Hardouin (1646–1729), the critic Élie Catherine Fréron (1719–71), and the physician René Laennec (1781–1826), inventor of the stethoscope.

The Constituent Assembly chose, as successor of the deceased Bishop Conan de Saint-Luc, Louis Alexandre Expilly, the Rector of the church of St. Martin at Morlaix.

He had himself elected president of the departmental Directory, but his increasingly moderate stance brought him under suspicion from the Jacobins.