On a bitterly cold December day in 1850 the Diocese of Mobile, less than 35 years old, celebrated its patronal feast, the Immaculate Conception, by consecrating a cathedral whose cornerstone had been laid in 1835. It represented a monumental expression of faith on the part of the Catholic community, led by Bishop Michael Portier (d. 1859), assisted by benefactors in France and Rome, and, closer to home, those whom one contemporary paper called "their fellow-citizens of every creed!" Bishop Martin John Spalding of Louisville who preached for the occasion said of the edifice: "It is almost worthy of God."

An heroic challenge was set by Bishop Portier in laying foundations for a church 162 feet in length and 90 feet in width. It met his vision for "the future of Mobile," and for the family of faith in Alabama and Florida which the Cathedral has served for more than 150 years. Subsequent generations met the promise of completing the church, sometimes following the original plan, but also in response to circumstances such as the fire of 1954 that could have destroyed the whole structure.