As bishop of the capital of Gaul, he was among the participants of the Council of Valencia of 374 regarding religious discipline of the clergy and the faithful.

Some time after the Council of Aquileia, an incident took place where an insane individual in a violent fit, had attacked and killed several people in the streets of the city with a sword.

At length a city magistrate arrived and persuaded Bishop Justus to hand the accused over to him, giving his word that the matter would be handled according to law.

[5] The bishop came to believe that his failure to adequately protect the murderer had made him unworthy to continue to lead the Christian community, and he resolved to devote the remainder of his life to doing penance.

His friends could neither convince him that he was not responsible for the unfortunate man's death, nor to reconsider his decision of being unworthy to be bishop.

The story is told then of a pilgrim in North Africa who some years later recognized Justus and reported this on his return to Lyon.

The city folk being eager to regain their bishop, sent a delegation led by Antioch, a priest of Lyon, to find him and bring him back to his diocese.

[5] At the end of the 4th century, a Vita Sancti Justi, Lugdunensis Episcopi, retracing in a hagiographic style the life of Justus, was written by a priest of Lyon.

Lyon was founded in 43 BC as the Roman Lugdunum, on the site of a Gallic trading settlement that already had a shrine to the god Lugh.

Stephen C. McCluskey says the August festival of Saint Justus, falling so close to the celebration of the harvest festival Lughnasadh, served to reinforce the Christianization of long-standing local traditions, which began with the dedication of the bishop's church to the Maccabees, whose feast day was celebrated on August 1.