On May 21, 1954,
Pope Pius XII appointed Byrne
auxiliary bishop of the Roman Catholic Archdiocese of Saint Louis, and he was consecrated on June 29, 1954. Archbishop
Joseph E. Ritter was the consecrator, with Bishop
Mark Carroll and Bishop
John Cody as primary co-consecrators. Upon
Mark Carroll's retirement on February 15, 1963, Byrne became the apostolic administrator
sede plena (), with Carroll retaining the office of archbishop. The episcopal advisor of the National Laywomen's Retreat Movement, he was seen as a "staunch defender" and proponent of the rights of women in the church. In 1971, he began service as the vice-president of the
National Conference of Catholic Bishops. He attended the
Second Ordinary General Assembly of the Synod of Bishops in 1971. His funeral was on October 25, 1974, at the
Cathedral of Saint Paul, and he was buried at
Resurrection Cemetery. ==References==