St. Firminus was born circa 480 in Narbonne, France on October 11. He was born to the senator and aristocrat Tonnatius Ferreolus, otherwise known as Tonance Ferréol the Second, and his wife Industria.
St. Firminus was well-educated by his 80-year-old uncle, Roricius (Ruricius or Rorice), who was a patrician. His uncle served as the third bishop of Uzès from 533 to 538. St. Firminus thereafter succeeded his uncle as bishop of Uzès.
In 538, he signed the fourth and fifth Councils of Orléans in 541 and 549, respectively. In 551, he assisted at the second council of Paris. At the time, the bishop of Uzès was under the metropolitan Archdiocese of Arles. St. Firminus was a spiritual student of Saint Cæsarius of Arles.
He died 15 years after he became bishop, in 553.
Saint Firminus is locally venerated as Saint Firmin and his relics are located in the Uzès Cathedral.