He continued his studies at the Vilnius University, in which in 1622 he received the title of Master of Philosophy. Later Parchevsky earned a doctorate in theology and was ordained to the priesthood in 1628, became rector in Starodub. In 1630 became the administrator of the Diocese of Smolensk.
During the war between the Commonwealth and the Russian kingdom from 1632 to 1634 remained besieged in Smolensk.
In 1635 Wladyslaw IV Vasa appointed him as the first bishop of Smolensk, and then Parchevsky went to Rome to obtain the approval of the new diocese, which was received on September 1, 1636. On September 7 of the same year he was ordained a bishop by Cardinal Giovanni Battista Pamphili, which in 1644 became Pope Innocent X. At the end of 1649 became bishop of Žemaičiai.
In 1651 carried out a visitation of the diocese. During the Swedish Deluge on 18 August 1655 signed the instrument of surrender of the Golden Horde Karl X Gustav.
On October 20 of that year, he signed a deed Swedish-Lithuanian union in Kaidan.
Peter Parchevsky died on 6 December 1658.