Petar Ovčarević was an Ottoman and then Hungarian river flotilla commander, who during his Ottoman service spied and informed the Christian army on the intentions and movements of the Ottoman army. His last years were spent in the Eastern Hungarian Kingdom, as one of the most notable magnates. Petar Ovčarević hailed from Belgrade, and was a hajduk. As a youngster he was captured by the Ottomans, but managed to have himself freed and join the Ottoman army. He for long served the Ottomans, then joined Hungarian service. He was a commander of the Šajkaši in Zemun, and during the Siege of Belgrade was the main commander of the Šajkaši in Belgrade. After surviving the siege, which ended in Ottoman takeover, and vacillating for a time, he joined the Ottomans and became a confidant of Ottoman general and sanjak-bey of Belgrade, Bali Bey Jahjapašić. He became a Martolos commander, commanding Serbs, based by the Belgrade rivers, inhabiting their own quarter and commanding a galley fleet. His unit was entrusted with the protection of Ottoman ferries on the Sava and Danube. Through Pavle Bakić, Ovčarević came into contact with Hungarian commander Pál Tomori, and helped the safe transfer of Bakić and his followers into Hungarian territory. He was a friend of Bakić, who seems to have assisted his secret crossing into Hungary a few months prior to the Battle of Mohács. It seems that his aid to Bakić led to loss of confidence, according to D. Popović, as the Serb crew was replaced by an Ottoman one. All this time he was in confidential service to both King Ferdinand I and John Zápolya and also representatives of other states, informing them of affairs in the Ottoman Empire. After Bali Bey's death, he rose further in rank and became the second-in-command and adviser of Bali Bey's younger brother and successor Mehmed Bey Jahjapašić, evidence of the very high trust he enjoyed. He greatly helped the Christian side in the war with the Ottomans by spying and sending secret reports to Hungarian commanders on the intentions and movements of the Ottoman army. Ovčarević was explicitly mentioned during the defense of the Buda fortress when Ferdinand I attacked at the end of 1530. He led 800 Serb and Turkish soldiers who arrived at Buda via the Danube. In 1531 Ferdinand's main confidant in Belgrade, the Ragusan Bocignolo, reported that Petar Ovčarević "participates in all consultation in the Belgrade Sanjak, especially those relating to the war, and that he for the second day informs him". Ovčarević informed Ferdinand through Bakić, whom he personally met, about affairs in the Ottoman Empire and Zapolya's country. In 1531 he and Stepko Vratković were in the company of Lasky, Zapolya's envoy, during negotiations with Rogendorf. It is unknown when he crossed into Zapolya's country. He received nobility status, and was mentioned in 1540 as the owner of Solymos and one of the most notable magnates in Zapolya's lands. After the death of Zapolya, he was the tutor of minor king John Sigismund, alongside Queen Isabelle and monk Đorđe Utešinović, and likely the commander of the Šajkaši. In 1541 he influenced Queen Isabelle into leaving Buda. His family, the Ovčarević, was one of the notable Serb noble families in Hungarian service in the 16th century. His kinsmen or descendants were Mihailo Ovčarević, a Šajkaši commander, Dimitrije Ovčarević, captain of Gyula, and Jovan Ovčarević, an emissary.
