11 October - Firmin is probably born in Narbonne. At the age of twelve, he comes to his parent Roricius, the third bishop of Uzès from 533 to 538. Firmin succeeds Roricius of Uzès on the latter's death in 538.

He subscribes to the fourth and fifth councils of Orleans. In 551, he attends the second council of Paris, at which time the bishopric of Uzès passes under the metropolis of Arles. In his turn, he had Ferréol, his nephew, raised, whom he designated as his successor. Firmin died on 11 October 553 and was buried in the church of Saint-Baudile in Nîmes, which he had built to the north of the city.

Firmin had a privileged relationship with Saint Césaire of Arles. Césaire was a monk of Lérins, and when he was ordained bishop of Arles, he built the first convent for women in Gaul. Firmin, his friend, was his disciple and also has his biographer. Firmin was particularly attracted to the consecrated life. He was a good shepherd, and he had the special gift of transmitting the teachings of the Church to the people. His teachings are simple and touching, and this opens to the Holy Spirit. By the way, Firmin said: "Without the Holy Spirit, Christ is just a story, and the Gospel will be mute and meaningless. The Church is only a structure. But with the Holy Spirit, then Christ is present, the Gospel is the power of life and the Church is the communion of the Trinity".