Prior to his elevation to the see of Vienne, little has been recorded about Mamertus' life. The fact that his brother, Claudianus Mamertus, the theological writer, received in his youth a sound training in rhetoric, and enjoyed the personal acquaintance of Bishop Eucherius of Lyons (434-50), suggests that the brothers belonged to a wealthy Gallic family from the neighbourhood of Lyons. Like his brother, St Mamertus was distinguished for his secular learning as well as theology, and, before his elevation to the episcopate, appears to have been married.