On May 8, 1881, Pope Leo XIII established the Diocese of Davenport. The Very Rev. John McMullen, the vicar general of the Archdiocese of Chicago and rector of Holy Name Cathedral, was chosen as the first bishop, and he made St. Margaret's his cathedral. A reception for him was held on July 30, 1881. A platform was built on the front of the church for the occasion. Bishop McMullen celebrated Mass for the first time in St. Margaret's Cathedral the following day. Father Cosgrove became the cathedral's rector and the vicar general of the diocese.