Monk in the Ukrainian Order of Saint Basil (Basilians) in Vilna at age 20 in 1604, taking the name brother Josaphat. Deacon. Ordained a Byzantine rite priest in 1609. 

    He became bishop of Vitebsk (now in Russia) at a relatively young age, and faced a difficult situation. Most monks, fearing interference in liturgy and customs, did not want union with Rome. By synods, catechetical instruction, reform of the clergy and personal example, however, Josaphat was successful in winning the greater part of the Orthodox in that area to the union.
    But the next year a dissident hierarchy was set up, and his opposite number spread the accusation that Josaphat had "gone Latin" and that all his people would have to do the same. He was not enthusiastically supported by the Latin bishops of Poland.

    Archbishop of Polotsk, Lithuania in 1617.

    While Josaphat attended the Diet of Warsaw in 1620, a dissident group, supported by Cossacks, set up an anti-Uniat bishops for each Uniat one, spread the accusation that Josaphat had "gone Latin," and that his followers would be forced to do the same, and placed a usurper on the archbishop's chair. Despite warnings, John went to Vitebsk, a hotbed of trouble, to try to correct the misunderstandings, and settle disturbances. The army remained loyal to the king, who remained loyal to the Union, and so the army tried to protect Josaphat and his clergy.

    Late in 1623 an anti-Uniat priest named Elias shouted insults at Josaphat from his own courtyard, and tried to force his way into the residence. When he was removed, a mob assembled and forced his release. Mob mentality took over, and they invaded the residence. Josaphat tried to insure the safety of his servants before fleeing himself, but did not get out in time, and was martyred by the mob. His death was a shock to both sides of the dispute, brought some sanity and a cooling off period to both sides of the conflict.