A military leader of the Polish–Lithuanian Commonwealth both on land and sea, Sahaidachny is best known for the significant role his troops played in the Battle of Khotyn against the Ottoman Empire in 1621, as well as the Polish Prince Władysław IV Vasa's attempt to usurp the Russian throne in 1618.

[9] Based on the assumption that in those days, children were usually named after a saint whose date of birth was close, Sahaidachny was roughly born around June 29 (July 9) 1582, on the feast of the apostles Peter and Paul.

[12] The city of Ostroh was a major center of Eastern Orthodox culture, theology and ideology, in which many works directed against Catholicism and the Ukrainian Greek Catholic Church, formed by the Union of Brest, were produced.

[16] War trophies, including cannons, jewels, as well as rich captives captured during looting expeditions, allowed the Cossacks to arm themselves well and act as a powerful military force.

[17] The Zaporozhians justified their activities primarily as protecting their native land from the enemy, which was carried out in the form of preemptive strikes on its territory and the liberation of Christian prisoners from captivity.

[19] In the autumn of 1600, the Great Crown Hetman Jan Zamoyski organized a Moldavian–Wallachian military campaign, which was joined by several thousand Cossacks led by Gavril Krutnevych.

Upon returning home, sensing their power and the helplessness of the crown government, the Cossacks resorted to looting, taking revenge on the nobility and burghers of Polotsk and Vitebsk, who helped the punitive troops suppress Severyn Nalivaik's rebellion.

Secondly, the attacks of the Zaporozhians caused colossal economic losses to the Ottoman Empire, reduced its military power, and also had a deterrent effect on the Tatars, as they limited their opportunities to devastate Ukrainian lands.

[25] The Zaporozhians carried out their sea campaigns under the political slogan of fighting the enemies of the Holy Cross, and their main target was rich Ottoman and Tatar cities.

This is known from the letter of Łukasz Sapieha, who complained to his brother Lew about Sahaidachny, who was in the Kyiv region and did not want to come to the aid of units of the Polish–Lithuanian Commonwealth and ordered his Cossacks to retreat.

[30][31] Shortly after being elected hetman, Sahaidachny prepared a campaign to the impregnable Ottoman fortress of Kaffa (modern Feodosia), which was the main slave market in the Crimea.

Wanting to avoid a battle, on September 23, the parties concluded a peace treaty, one of the clauses of which was the prohibition of the Zaporozhians from leaving the Dnieper River in the Black Sea.

In April 1618 in Warsaw, the ambassadors of the Zaporizhzhian Army generally agreed to the anti-Ottoman plan of the Persian Shah Abbas I the Great to relocate 10,000–12,000 Cossacks to the Black Sea port of Jani (perhaps at the mouth of the Trabzon River).

Therefore, the priests of Yelets asked the Zaporozhians not to destroy the city, offering instead to hand over the tsar's envoy S. Khrushchev together with the treasury (30 thousand rubles intended to bribe the Crimean Khan).

The first skirmishes near Zaraysk took place on September 11, when the Zaporizhians vanguard defeated a detachment of Moscovy soldiers, and the Cossacks even managed to break into the city prison.

On September 12, Sahaidachny received a letter from Prince Władysław, in which he indicated that he was leaving Mozhaisk for Moscow, and ordered the hetman to proceed immediately to arrive in the area of the Simon Monastery.

On September 28, the ambassadors arrived in Zvenigorod and during negotiations with the command of the Commonwealth of Nations, they agreed that the unification of the troops would take place on October 3 in the village of Tushino.

In the letter, the hetman writes: "May God almighty in the achievement of this plan for the honor of the kingdom assigned to your royal grace, be happy and blessed, and that people stubbornly under the feet of their majesty will contribute to subverting".

The army of Zaporozhian Cossacks was divided into several parts, some of them went to storm the fortress beyond the Moscow River, and the rest had to play the role of a reserve and distract the tsarist troops from the main directions.

Meanwhile, separate detachments of the Zaporozhians continued to attack Moscovy cities north and northwest of Moscow, ravaging the Yaroslavl and Vologda districts, thereby undermining the state's economic resources.

In this environment, the idea appeared, contrary to the prohibitions of the Polish–Lithuanian Commonwealth, to restore the Orthodox hierarchy of the Kyiv Metropolitanate, which was lost as a result of the Brest Church Union of 1596.

[55] On March 25, in Kyiv, the hetman with several thousand Cossacks solemnly met the Patriarch of Jerusalem, asking him on behalf of the entire Zaporizhzhian Army for forgiveness of sins for shedding the blood of Christians during the Moscow campaign of 1618.

A clear demonstration of the political support of the Orthodox Church was the entry of the Hetman together with the entire Zaporozhian Army into the Kyiv (Epiphany) Brotherhood, which took place between May 27 and June 5, 1620.

[56] In November 1620, P. Konashevych-Sahaidachny, together with the newly ordained bishop Yosif Kurcevych, spoke at the regular session of the Sejm of the Polish–Lithuanian Commonwealth, where he raised the question of royal recognition of the consecrations performed by Patriarch Feofan.

[56] In February 1621, Konashevych-Sahaidachny accompanied several hundred Cossacks to the Moldavian border of the Patriarch of Jerusalem Feofan III, who was returning home after the ordination of Orthodox hierarchs in Ukraine.

The Rada elected Yakov Borodavka, a representative of unregistered Cossacks, as hetman and accepted the proposal of the Sejm of the Polish–Lithuanian Commonwealth to take part in the war against the Ottoman Empire.

[61] Considering the numerical superiority of the Ottoman army in terms of manpower and artillery, Sahaidachny decided to launch a night war, which not only inflicted significant losses on the enemy but also undermined his morale.

At the end of his life, he contributed to the renewal of churches in Kyiv, the construction of a new one in the Floriv Monastery, he sent fifteen-thousand red and gold coins to the Lviv Fraternal School.

In 2023, according to the Department of Cultural Heritage Protection of the KMDA, on the territory of the Kyiv-Mohyla Academy, archaeologists will conduct excavations at the site of the remains of the Epiphany Cathedral and try to find the grave of Hetman Peter Sahaidachny.

In 2011, by the decision of the Synod of Bishops of the Ukrainian Autocephalous Orthodox Church, Petro Sahaidachny was canonized at the local level in the rank of "pious hetman".