Their father Severianus is claimed to have been a dux or governor of Carthago Spartaria, according to their hagiographers, though this seems more of a fanciful interpretation since Isidore simply states that he was a citizen.

The children's subsequent public careers reflect their distinguished origin: Leander and Isidore both became bishops of Hispalis (Seville), and their sister Florentina was an abbess who directed forty convents and one thousand nuns.

[2][3] The Chalcedonian hierarchy were in contact with representatives of the Eastern Roman or Byzantine emperor, who had maintained a considerable territory in the far south of Hispania ever since his predecessor had been invited to the peninsula by king Athanagild several decades before.

As bishop he had access to the Chalcedonian Merovingian princess Ingunthis, who had come as a bride for the kingdom's heir, and he assisted her to convert her husband Hermenegild, the eldest son of Liuvigild, an act that cannot honestly be divorced from a political context.

Pierre Suau puts it, "In endeavoring to save his country from Arianism, Leander showed himself an orthodox Christian and a far-sighted patriot.

It is possible, but not proven, that he sought to rouse the Byzantine Emperor Tiberius II Constantine to take up arms against the Arian king; but in any case the attempt was without result.

Leander delivered the triumphant closing sermon which his brother Isidore entitled Homilia de triumpho ecclesiae ob conversionem Gothorum ("a homily upon the triumph of the Church and the conversion of the Goths").