Sancho was a son of James I of Aragon and his second wife Yolanda of Hungary.
He joined the Order of the Blessed Virgin Mary of Mercy at a young age and had Peter Pascual as a tutor.
In 1275 he raised some troops to engage Marinid armies that had attacked Andalusia.
On 21 October 1275 he tried to intercept a numerically superior Marinid army in the battle of Martos but was defeated and taken prisoner.
Because of his heroic death, he was venerated by the people as a martyr and considered Blessed.