He emigrated to the United States in 1844 and was ordained to the priesthood for the Roman Catholic Diocese of Cincinnati on August 30, 1852. He was named Bishop of Mobile on September 26, 1859, and consecrated on December 4, 1859, by Archbishop Antoine Blanc in Saint Louis Cathedral, New Orleans. In his diocese he found twelve churches and fourteen schools for which he had only eight secular priests and he therefore brought from Ireland eleven young candidates for the priesthood.
Bishop Quinlan"s administration fell upon the storm days of the American Civil War.
After the battle of Shiloh, he hastened on a special train to the blood-stained battle-ground and ministered to the temporal and spiritual wants of North and South. After the war diocesan activities were crippled.
Nevertheless, besides repairing ruined churches, Bishop Quinlan built the portico of the Mobile cathedral, founded Saint Patrick"s and Saint Mary"s churches in the same city, and established churches in Huntsville, Decatur, Tuscumbia, Florence, Cullman, Birmingham, Eufaula, Whistler, and Toulminville. In April 1876, Bishop Quinlan invited the Benedictines from Saint Vincent"s Abbey, Pennsylvania to the diocese, and they settled at Cullman, Alabama.
He died March 9, 1883, and is entombed under the portico of the Cathedral Basilica of the Immaculate Conception in Mobile, Alabama.
Quinlan Hall, on the campus of Spring Hill College, is named in his honor.