While little is known of St. Delphinus before his elevation to the episcopal see of Bordeaux in France, as a bishop he soon became renowned for his vigilance in defense of the Truth.

The saintliest princes of the Church at the time were honored to be counted among his friends and to correspond with him, among them, St. Ambrose of Milan.

He was present at the Council of Saragossa in 380, at which the Priscillian heresy was condemned. This heresy argued that the renunciation of marriage and the acceptance of asceticism were prerequisites for following Christ.

St. Delphinus later assembled a Council at Bordeaux, his episcopal city, whose assembly also condemned the same errors. Such was the force and zealous preaching of the Bishop of Bordeaux against those that propagated this heresy in his territory that it undermined their influence entirely and they soon abandoned the region for Italy.

In 388, St. Delphinus baptized the future Bishop of Nola, St. Paulinus, and inspired in him the desire to live a life of perfection. St. Paulinus spoke of him as his father and master.

In several letters, St. Paulinus speaks of St. Delphinus as his father and his master. The saintly Bishop of Bordeaux died on Christmas Eve in the year 403 becoming his feast day.