Born in Nájera, La Rioja, towards the year 1010. Son of Sancho Garcés III the greater, who inherited the title of King of Pamplona and Najera, on 18 October 1035, reigned in the year 1035 to 1054. He/She was married to Doña Estefanía Berenguer de Foix, daughter of the counts of Barcelona, with whom he/she had ten children of which six were male. He/She went to the aid of his brother, King Fernando I, in their territorial fights with the King of León, Bermudo III; Fernando, in gratitude towards his brother, ceded from the Bay of Santander to the Montes de Oca, including the lands of Alava, Guipuzcoa and Vizcaya.
It is regarded as a great warrior, firm Knight and noble swords, conquered definitively Calahorra to Arabs, in April 1045. From Calahorra he/she ravaged Allied Aragonese lands of his brother Fernando, that irrupted them. He/She was known as Najera's because in this villa, he/she founded the monastery of Santa María la Real, because according to tradition, found a day of hunting in a cave an image of the Virgin with a campaign and a dove at his feet.
The cast of the old County of Castile, led to the two brothers to the confrontation by the borders of both kingdoms, and was defeated and killed at the battle of Atapuerca, Burgos, September 1, 1054, on the same day that was proclaimed successor his son Sancho Garcés IV. His body was moved and buried in the Pantheon of Kings of Santa María de Nájera, which he/she himself had commissioned two years earlier. His wife, Doña Estefanía, played an important role, because it calmed tempers of the Christian Kings, with that averted potential infighting until his death.