Blanche was the second eldest daughter of King Charles III of Navarre[2] and infanta Eleanor of Castile.

Martin had been in need of legitimate heirs, as he had survived his previous wife and former co-ruler, Queen Maria of Sicily, and their only son.

Upon her return to Navarre, Blanche was sworn in as heir to the throne in Olite the 28 October 1415 and was given allegiance by the lords.

On 6 November 1419, Blanche married her second husband, John,[2] duke of Peñafiel, the second son of Ferdinand I of Aragon and Eleanor of Alburquerque, by proxy in Olite.

Don Juan Vélaz de Medrano, Lord of Igúzquiza, royal chamberlain of the Kings of Navarre and Aragón, accompanied Queen Blanche I on a pilgrimage to Santa María del Pilar in 1433.