He was born on 23 August 1918 in Sanok into a wealthy family with noble origins (of the Jastrzębiec coat of arms). His father Zygmunt and his wife Maria ran a patisserie café, which was small but informally considered the social centre of the town.

He became involved with scouting as early as 1928. He was gaining ranks and skills (in 1938 he was awarded the rank of assistant scoutmaster) and engaging in scouting activities, training subordinates at courses, camps and training sessions. He was, for instance, an instructor at the Scout School in Górki Wielkie near Skoczów, which was then headed by the author of "Stones for the rampart", Aleksander Kamiński.

After passing his school-leaving examination in 1938 at the Queen Sophia State Middle School for Boys in Sanok, he entered the Cavalry Reserve Cadet Officer School in Grudziądz. After completing it, just before the outbreak of World War II, he was sent to the 20th King Jan III Sobieski Uhlan Regiment in Rzeszów.

After the USSR's aggression against Poland on 17 September 1939, his regiment, based in a palace in Pomorzany, was surrounded by Soviet troops and his soldiers were captured by the Soviets. At the turn of October and November 1939, Zdzislaw Peszkowski, together with other officers, was transported to the Kozielsk camp. Peszkowski and a small group of prisoners avoided the fate of the Polish soldiers shot by the Soviets in the Katyn forests in the spring of 1940. As he recalled:

"There were 232 of us who survived from Kozelsk, from the entire camp. The last transport. We saw everyone off and said goodbye, until finally we too were taken outside the gates of the monastery – the captivity camp. It was a providential act of God that this last transport survived. We were sent to Pavlishchev-Bor and then to Griazovets. There we lived to see the "amnesty" and, after being drafted into the Polish Army under General Władysław Anders, we left Russia."

After the Soviets agreed to form a Polish army in the USSR, Peszkowski arrived in Tockoye on 9 September 1941 and was assigned to the 1st Krechowce Uhlan Regiment of General Michał Karaszewicz-Tokarzewski's division. He was promoted to the rank of lieutenant and then to cavalry captain. Following the route with General Anders's army through Iraq, Iran, India, Egypt, Lebanon, Syria, Lebanon, Italy, to England, he commanded a company in the 1st Krechowce Uhlan Regiment. As a cultural and educational officer, he organised religious and patriotic celebrations and formed the "Horseshoe" scout circle. In Iraq, he earned the rank of scoutmaster, and among refugee youth in Tehran, Isfahan, Karachi, Palestine and then in India, in the Polish town of Valivade, he organised scout life. With effect from 15 September 1946, he was appointed Deputy Commandant of the Polish Scout Association in the East and Visitor of Scout Education in India.

After the end of the Second World War, he remained in exile. In 1948, he began his studies in psychology and philosophy at the University of Oxford. In 1949, he went to Rome to study at the Pontifical Gregorian University, but already in 1950, he moved to the Polish SS. Cyril and Methodius Seminary in Orchard Lake at the University of Wisconsin in Detroit. It was there that he obtained his master's degree in theology. On 5 June 1954, he was ordained a priest at Detroit Cathedral.

He began his teaching and research work at the faculty of the Polish Institutes of Research in Orchard Lake. From this university, he carried out extensive collaboration with various academic institutions, including the Polish American Historical Association. He performed pastoral duties as chief chaplain of the Polish Scouting Association abroad. He also became chaplain to the Katyn Families.

In 1990, Rev. Msgr. Zdzislaw Peszkowski returned to Poland for good. He then undertook intensive efforts to commemorate the Katyn massacre. He was the initiator of the International Katyn Year, announced in 1995, and founder and president of the "Golgotha of the East" Foundation, which, among other things, led to the establishment of military cemeteries in Katyn, Kharkiv and Miednoye.

On 26 January 2006, the Sejm of the Republic of Poland adopted a resolution officially supporting the candidature of Rev. Zdzisław Peszkowski for the Nobel Peace Prize. The justification also mentions that, in addition to being active in preserving the memory of the victims of the Katyn massacre, "the Prelate – a former Soviet prisoner and a would-be victim of Katyn – has for years been actively promoting Polish-Russian reconciliation".

He died on 8 October 2007 in Anin. He was laid to rest in the crypt in the Pantheon of Great Poles in the Temple of Divine Providence in Warsaw. The tombstone inscription features the scouting greeting "Be Prepared."