Cronin grew up in the U.S. and Canada, and moved to the Midwestern United States after the American Civil War. He became a physician and a prominent member of high society, and represented St. Louis at the Exposition Universelle (1878). While in St. Louis, Cronin joined multiple clubs, among them, the Irish nationalist organization, Clan na Gael. When he moved to Chicago, Cronin continued his involvement with Clan na Gael. After criticizing the leadership of the Chicago camp of Clan na Gael, he was expelled from the group and accused of being a British spy. In May 1889, Cronin disappeared. Later that month, public works employees discovered his body in a sewer in a northern suburb of Chicago. The press coverage of the investigation and trial caught international attention. Cronin's funeral drew the largest crowds for a funeral since the arrival of Abraham Lincoln's body in Chicago. Patrick O'Sullivan, Daniel Coughlin, Martin Burke, and John Kunzel were found guilty of the murder of Patrick Cronin.