[1] Sancho was born in Coimbra, the eldest son of Afonso II of Portugal by his wife, Urraca of Castile.

His father, Afonso II, had been excommunicated by Pope Honorius III, for his attempts at reducing the Church's power within the country.

From 1236 onwards, Sancho II conquered several cities in the Algarve and Alentejo, securing the Portuguese position in the region.

Sancho II proved a capable commander but, with regard to equally important administrative issues, he was less competent.

Since the Church was the dominant power of the 13th century, Pope Innocent IV felt free to issue bull Grandi non immerito, ordering the Portuguese to choose a new king to replace the so-called heretic.