John Hennessy was born on July 19, 1847, near Cloyne, County Cork, in Ireland to Michael and Ellen (née Cronin) Hennessy.[1] In 1850, the Hennessy family immigrated to the United States, settling in St. Louis, Missouri.[2] He received his early education at the local cathedral school and the Christian Brothers College in Town and Country, Missouri, graduating there in 1862.[2] Hennessycompleted his theological studies at St. Francis Seminary in Milwaukee, Wisconsin, and his philosophical studies at St. Vincent College in Cape Girardeau, Missouri.[1]
Hennessy was ordained to the priesthood in St. Louis by Bishop Joseph Machebeuf for the Archdiocese of St. Louis on November 28, 1869.[3] At age 22, he was below the age required for ordination, but was granted a dispensation by Pope Pius IX.[1]
After his ordination, the archdiocese assigned Hennessy as pastor of a parish in Iron Mountain, Missouri, with his jurisdiction extending as far south as Arkansas.[2] Over the next few years, he erected churches in Missouri at Bismarck, Doniphan, Poplar Bluff, Gatewood, Graniteville, and Farmington.[1] Hennessy established the Catholic Railroad Men's Benevolent Union in 1871, a convent for the Ursuline Sisters at Arcadia, Missouri, in 1877, and the first total abstinence society in southeast Missouri.[2]
In 1878, Hennessy was elected procurator and vice-president of the Catholic Protectory for Boys at Glencoe, Missouri.[1] He was named rector of St. John's Church in St. Louis in 1880.[2] That same year, he became editor of the St. Louis Youths' Magazine and in 1882 secretary of the St. Louis Orphan Board.[1] He also served as treasurer of the diocesan clergy fund and spiritual director of the St. Vincent de Paul Society.[1]
On February 11, 1888, Hennessy was appointed the first bishop of the newly erected Diocese of Wichita by Pope Leo XIII.[3] He was technically the second Bishop of Wichita, as Reverend James O'Reilly had been appointed as bishop in 1887, but he died before his consecration.[4] Hennessy was consecrated at St. John's Church in St. Louis on November 30, 1888, by Archbishop Peter Kenrick, with Archbishop John Hennessy and Bishop Louis Fink serving as co-consecrators.[3]
In 1890, Hennessy persuaded the Sisters of the Sorrowful Mother to come to Kansas and take over management of St. Francis Hospital in Wichita.[5] In 1898 he convened the first diocesan synod.[6] He broke ground for the Cathedral of the Immaculate Conception in Wichita in April 1906 and laid the cornerstone the following October; it was dedicated by Cardinal James Gibbons in September 1912.[6] Between 1891 and 1898, Hennessy also served as apostolic administrator of the Diocese of Concordia in Kansas.[3]
On July 13, 1920, Hennessy suffered a stroke and died in Wichita a few hours later. He was interred in the Cathedral of the Immaculate Conception.[7]