When his son opposed him in 517, he had him killed. Because of this, Sigismund retreated to the monastery of Saint-Maurice in Agaune, that he had founded a couple of years earlier.

In 523, he led the Burgundian army against the invading Franks. He was captured, taken to Orleans and killed. Afterwards, he was honoured by the Burgundians as a martyr, and eventually canonized.