His reign was occupied with attempts to strengthen the crown against the Union of Aragon and other such devices of the nobility, with their near constant revolts, and with foreign wars, in Sardinia, Sicily, the Mezzogiorno, Greece, and the Balearics.

Peter was born at Balaguer,[1] the eldest son and heir of Alfons IV, then Count of Urgell, and his first wife, Teresa d'Entença.

En route he stopped at Lleida to affirm the Usatges and Constitutions of the Principality of Catalonia and receive the homage of his Catalan subjects.

[3] While in Valencia he decided on the case of his stepmother's inheritance, depriving her of income and outlawing her Castilian protector, Peter Ponce of León and Jérica.

[4] In May 1339 he allied with Alfonso XI of Castile against Morocco, but his contribution of a fleet had no effect at the pivotal Battle of Río Salado (October 1340).

[3] The rising economic star of Majorca, whose merchants were establishing independent markets and gaining trading privileges in the western Mediterranean, threatened the supremacy of Barcelona.

[3] Peter's outrage, however, was given no outlet until 1341, when James, threatened with invasion by the French over disputed rights to the Lordship of Montpellier, called on his suzerain Aragon for aid.

[8] Though James sued for peace and Pope Clement attempted to mediate it, Peter returned to Barcelona prepared to invade Roussillon and Cerdagne.

[7][8] By the Pact of Madrid, Peter was constrained to aid Alfonso XI of Castile in his successful attack on Algeciras (1344) and his failed attempt on Gibraltar (1349) by defending against a Moroccan counterattack.

Peter decided that he would instead name his daughter Constance as his heir presumptive notwithstanding the precedents established by James I and Alfonso IV to exclude females from the throne.

Peter eventually succumbed to the pressure to hold a cortes in Zaragoza where he made numerous concessions of royal authority to quell a rebellion he was not yet in a position to crush.

Assembling an army of increasingly powerful royalists in Aragon, Peter attacked the unionist forces at the Battle of Epila on 21 July 1348.

At the Catalan Courts celebrated at Barcelona, Vilafranca del Penedès and Cervera in 1358–1359, Peter instituted the Deputation of the General or Generalitat.

Castile had recently invaded Aragon and Valencia and the cortes decided to streamline the government by designating a dozen deputies to oversee the fiscal and material policies of the Crown.

Toward the end of his reign (c. 1370) Peter ordered the compilation of the Chronicle of Sant Joan de la Penya to record the historical basis for the authority of the crown.

According to historical record, Peter IV of Aragon and his Jewish physician had a friendly disputation regarding the question of why the Jews were not allowed to drink kosher wine touched by a Christian.

[9][10][11] In 1350, in response to the black plague, Peter IV ordered the mayor of Lleida to construct a new Jewish cemetery, as the existing one became overwhelmed by the number of new corpses.