[1] Deciding that he wanted to become a priest, Callahan applied to the Archbishop Quigley Preparatory Seminary in Chicago, but was rejected.

[3] Callahan then attended Loyola University Chicago, obtaining a bachelor's degree in radio and television communications in 1973.

[4] Callahan was ordained to the priesthood in Milwaukee at the Basilica of St. Josaphat for the Minorites by Archbishop William Cousins on April 30, 1977.

[6] Following Dolan's appointment as archbishop of the Archdiocese of New York in February 2009, Callahan was elected as the diocesan administrator of Milwaukee on April 20, 2009.

He oversaw the daily administration of the archdiocese until Benedict XVI named Bishop Jerome Listecki as the new archbishop in November 2009.

He encouraged Catholic Democrats to “repent of your support of that party and its platform or face the fires of hell.” In July 2021, Callahan removed Altman as pastor of St. James and banned him from public preaching.

[10][11][12] The next day, in defiance of Callahan's order, Altman gave the benediction at the 2021 Conservative Political Action Conference (CPAC) in Orlando, Florida.