[2][3] Peter Krešimir was born as one of two children to king Stephen I (Stjepan I) and his wife Hicela, daughter of the Venetian Doge Pietro II Orseolo.

[5] From the outset, he continued the policies of his father,[6] and was immediately requested in letter by Pope Nicholas II first in 1059 and then in 1060 to further reform the Croatian church in accordance with the Roman rite.

[10] This caused a rebellion of the clergy led by a bishop of Krk Cededa and a certain priest named Vuk (Ulfus),[10] who had presented the demands and gifts of the Croats to the Pope during his stay in Rome, but was told nothing could be accomplished without the consent of the Split see and the king.

Krešimir harshly quelled all opposition and sustained a firm alignment towards western Romanism, with the intent of more fully integrating the Dalmatian populace into his realm.

As the king was at that time preoccupied with the liturgical issues and reforms in Dalmatia, these parts were eventually liberated by his ban Demetrius Zvonimir.

Older generation of historians like Ferdo Šišić and Miho Barada assumed, apart from the ban of Croatia, that the banate of Slavonia existed during this period, and that was held by Krešimir's successor Demetrius Zvonimir.

[19] In 1069, he gave the island of Maun, near Nin, to the monastery of St. Krševan in Zadar, in thanks for the "expansion of the kingdom on land and on sea, by the grace of the omnipotent God" (quia Deus omnipotens terra marique nostrum prolungavit regnum).

In his surviving document, Krešimir nevertheless did not fail to point out that it was "our own island that lies on our Dalmatian sea" (nostram propriam insulam in nostro Dalmatico mari sitam, que vocatur Mauni).

Only after the monarch and 12 Croatian župans had taken an oath that he did not kill his brother, the Pope symbolically restored the royal power to Krešimir.

At the time, the Byzantine empire was at war both with the Seljuk Turks in Asia and the Normans in southern Italy, so Krešimir took the opportunity and, avoiding an imperial nomination as proconsul or eparch, consolidated his holdings as the regnum Dalmatiae et Chroatia.

[24] It seems that Petar Krešimir died in a Norman prison by November 1074 because on 25 January 1075 was sent a letter by Pope Gregory VII to Sweyn II of Denmark in search of a candidate for a new ruler of, to the Pope, nearby "rich land by the sea which became mastered by vulgar and cowardly heretics", meaning Croatia and Amico's Normans.