Mikalai Korsak was born near Navahrudak from a nobleCalvinist family. Primaries sources disagree on his birth year, which anyway can be fixed into a range from 1598 to 1601. He studied by the Jesuits in Niasviž and in Vilnius, and later in Papal Missionary College in Braniewo and by the Jesuits in Prague. By the Jesuits he converted to the Latin Church and later, supported by Metropolitan Jazep Velamin-Rutski, he joined the Greek-Catholic Church. In 1620 he entered in the Order of Saint Basil the Great taking the religious name of Rafajil and he passed his year of novitiate in the monastery of Byten. He studied in the Greek College in Rome from December 1621 to November 1624, when he was requested to return in his country to serve as a bishop. In 1625 Korsak became archimandrite of the monastery of the Holy Trinity in Vilnius, in 1626 Proto-Archimandrite of the whole order and in September 1626 he was consecrated a bishop with the title of Galicia. Metropolitan Rutsky chose him as coadjutor bishop with right of succession, and so he was confirmed by Rome on 9 March 1631 notwithstanding the initial concern of the King for his young age. In 1632 he became Eparch of Pinsk. In 1632 the situation of the Greek-Catholic Church had a downturn because of the death of the King Sigismund III who had supported the Church since the Union of Brest. The new king, Władysław IV, to be elected signed the "Pacta Conventa" which were favorable to the Orthodox faction, supported by the Cossaks, and prejudicial to the Greek-Catholic Church. Korsak was sent to Rome to find support for the position of his Church, as he succeeded to do. He remained in Rome from 1633 to 1635. Metropolitan Rutsky died on 5 February 1637 and Korsak became the new Metropolitan of Kiev and head of the Greek-Catholic Church. As his predecessor, he went on in negotiations with the Orthodox Metropolitan of Kiev, Peter Mogila about the way to unify the Ukrainian Church, but in 1639 he had to return to Rome for the third time, requested to visit the pope. He arrived in Rome in September 1639, and he passed the winter there. In 1640 he fell ill, and he died in Rome on 28 August 1640. He was buried in the Greek Rite church of Santi Sergio e Bacco. He wrote a biography of Metropolitan Rutsky, and he translated in Latin the works of Meletius Smotrytsky.
