[6] While attending Kenyon College in Gambier, Ohio in 1845, he received a letter from William Rosecrans announcing his conversion to Catholicism.

[3] Influenced by his brother's conversion, Rosecrans converted to Catholicism that same year, being ministered to by Jean-Baptiste Lamy while the latter was serving as a missionary priest in the area.

Archbishop John Purcell sent him to Rome to study at the Pontifical Urbaniana University, where he earned his Doctor of Theology degree.

[7] He was then assigned as a curate at St. Peter in Chains Cathedral Parish and as a professor at Mount St. Mary's Seminary of the West, both in Cincinnati.

[8] He received his episcopal consecration on March 25, 1862, from Archbishop Purcell, with Bishops Martin Spalding and John Luers serving as co-consecrators, at St. Peter's Cathedral.

[2] During his 10-year-long tenure, Rosecrans founded St. Aloysius Seminary for young men in 1871, dedicated the diocese to the Sacred Heart in December 1873, and established the diocesan newspaper, The Catholic Columbian, in 1875.