Petras Jonaitis Mantigirdaitis (died after 1497) was a prominent noble of the Grand Duchy of Lithuania. Grandson of Petras Mantigirdaitis, he first appeared in written sources in 1476 and reached his career high in 1490s when he was Voivode of Trakai (1490–97) and Grand Marshal of Lithuania (1491–97). Chronicler Marcin Bielski described that Alexander Jagiellon was crowned and blessed as the new Grand Duke of Lithuania by the Bishop of Vilnius in 1492. Then Mantigirdaitis presented Alexander with a naked sword and a reminder that Alexander was elected to be a just ruler. In 1494, Mantigirdaitis was sent on the diplomatic mission to negotiate peace with the Grand Duchy of Moscow and marriage of Helena of Moscow to Alexander to end the First Muscovite–Lithuanian War. The Bychowiec Chronicle names him as a Great Hetman who recommended Konstantin Ostrogski, the first official Great Hetman, after his death. Therefore, it is likely that at some point Mantigirdaitis was the commander of the Lithuanian army.
Mantigirdaitis held the following offices:
- Starosta of Braslaw (1476–82) and Lutsk (1486–89)
- Marshal of Grand Duke (1480–82) and Volhynia (1487–89)
- Voivode of Trakai (1490–97)
- Grand Marshal of Lithuania (1491–97)
Mantigirdaitis was married twice. His first wife was Anna, daughter of Jonas Vėževičius, regent of Smolensk. They had a son and a daughter. Their son Jonas died in the Battle of Vedrosha ending the family line. Their daughter Sophia married Stanisław Kiszka, who inherited the family's substantial wealth. Mantigirdaitis' second wife was Anna, daughter of Alexander Olshanski; they had no children. In 1482, Anna funded the Chapel of Holy Trinity in Vilnius Cathedral. It is likely that Mantigirdaitis funded the Catholic church in Iwye, his most important estate.