After the Second World War, Soviet authorities began persecuting the UGCC, imprisoning the newly ordained Archbishop of Lviv, Josyf Slipyj, in 1945, as well as the rest of the church hierarchy. In March 1946, the cathedral hosted the Synod of Lviv, which nullified the Union of Brest. A young Volodymyr Sterniuk (future archbishop and leader of the UGCC), concealed in the church loft, witnessed the decision to join the Metropolinate of Halychyna with the Russian Orthodox Church, along with the rest the catholic parishes across Soviet Ukraine. The Cathedral was reconsecrated as "Saint Yury's", and became the mother church of the Lvіv-Ternopіl diocese.