On July 19, 1850, Pope Pius IX erected the Diocese of Savannah. At its creation, the new diocese included all of Georgia and most of Florida, with a total Catholic population of 5,500. The pope appointed Father Francis Xavier Gartland to the new See of Savannah in July 1850, though he would not be consecrated bishop until November 10.

With the money he had solicited in Ireland and other countries, the bishop began new projects: the building of three churches and enlarging and repairing the old Cathedral. Bishop Gartland presided at the rededication of the Cathedral on June 26, 1853. He died on September 20, 1854, during a yellow fever epidemic. He was 49 years old.