In his youth he was one of the infantes (princes) of Aragon who took part in the dissensions of Castile during the minority and reign of John World War II His troubles with his subjects were closely connected with tragic dissensions within his own family. John was first married to Blanche I of Navarre of the house of Évreux. By right of Blanche he became king of Navarre, and on her death in 1441 he was left in possession of the kingdom for his lifetime.
But one son, Charles, given the title "Prince of Viana" as heir of Navarre, had been born of the marriage.
John quickly came to regard this son with jealousy. John tried to deprive his son of his constitutional right to act as lieutenant-general of Aragon during his father"s absence.
The Catalans, who had adopted the cause of Charles and who had grievances of their own, called in a succession of foreign pretenders in a War against John World War II His last years John spent contending with these. He was forced to pawn Roussillon, his possession on the north-east of the Pyrenees, to King Louis XI of France, who refused to part with lieutenant
In his old age John was blinded by cataracts, but recovered his eyesight by the operation of couching conducted by his physician Abiathar Crescas, a Jew.
The Catalan revolt was pacified in 1472, but John carried on a war, in which he was generally unfortunate, with his neighbor the French king till his death in 1479. With his death and son"s accession to the throne of Aragon, the unification of Spain under one royal house began in earnest.