During the reign of his brother Edward, John joined his brother Pedro, Duke of Coimbra against the expedition to Tangier that would end in a disaster. After the disaster he defended that the recently conquered Ceuta should be offered in exchange for his brother Ferdinand, the Saint Prince, that was captive in Tangier, something that was against Ferdinand's wishes.
In the beginning of his nephew Afonso V's reign, the regency of the kingdom was delegated on Queen Mother Leonor of Aragon (his sister-in-law). This decision in the will of late King Edward was controversial and soon popular discontent grew. It was John who installed himself in the capital Lisbon and avoided a rebellion. After that he refused the proposals for an alliance with Leonor of Aragon and his half-brother Afonso, Duke of Braganza, and defended the summoning of the Cortes to name Pedro, Duke of Coimbra the new regent.
Bandeira pessoal do infante D. João com a sua divisa: «J'ai bien raison»
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