He became a priest of that church in about 387 or 388, after the death of Valerianus, bishop of that city. He was one of the most celebrated prelates of his time and was in active correspondence with contemporaries St. Ambrose, St. Jerome, and Tyrannius Rufinus.
As a scholarly theologian, he urged these friends to produce learned works. St. Ambrose was encouraged by him to write exegetical works; St. Jerome dedicated to him translations and commentaries, which he had written at his suggestion (translations of the Books of Paralipomenon, Tobit, the books of Solomon, commentaries on the Prophecy of Habakkuk). In the bitter quarrel between St. Jerome and Rufinus concerning Origenism, Chromatius, while rejecting the false doctrines of Origen of Alexandria, attempted to make peace between the disputants.
He maintained ecclesiastical communion with Rufinus and induced him not to answer the last attack of St. Jerome, but to devote himself to new literary works, especially to the translation of the Ecclesiastical History of Eusebius.
Chromatius opposed Arianism with much zeal and rooted it out in his diocese. He gave loyal support to St. John Chrysostom, Archbishop of Constantinople, when unjustly oppressed, and wrote in his favour to Honorius, the Western emperor, who sent this letter to his brother, Arcadius. This intercession, however, availed nothing.
Chromatius was also active as an exegete. Until the modern age only seventeen treatises were known to be authored by him on the Gospel according to St. Matthew (iii, 15-17; v-vi, 24), besides a fine homily on the Eight Beatitudes (counted as an eighteenth treatise). In 1969 researcher Henri Lemarié discovered and published thirty-eight sermons.
His feast is celebrated 2 December.