The Fifth Provincial Council of Baltimore, which was held in May 1843, recommended the erection of the Diocese of Pittsburgh and nominated O'Connor as its first Bishop. When Pope Gregory XVI accepted the recommendation, O'Connor traveled to Rome for consecration as a bishop, but he petitioned the pope to revoke his appointment and to allow him instead to enter the Jesuits instead. Pope Gregory, however, refused and said, "You shall be bishop first, and a Jesuit afterwards". He accepted the pope's will and was formally appointed the first Bishop of Pittsburgh on August 11, 1843. On August 15, he received his consecration from Cardinal Giacomo Filippo Fransoni at the Church of Sant'Agata dei Goti.