Cahill attended Regis High School in Manhattan, where he studied ancient Greek and Latin.
[1][2] He continued his study of Greek and Latin literature, as well as medieval philosophy, scripture, and theology, at Fordham University.
He ultimately decided not to pursue the priesthood, and went on to complete his Master of Fine Arts in film and dramatic literature at Columbia University in 1968.
[3] His manuscript for How the Irish Saved Civilization: The Untold Story of Ireland's Heroic Role From the Fall of Rome to the Rise of Medieval Europe was rejected by five publishing houses before it was accepted by Nan A. Talese at Doubleday in 1991.
[1] In anticipation of writing The Gifts of the Jews (1998), Cahill studied scripture at Union Theological Seminary in New York.
[3] Prior to retiring to writing full-time, Cahill was the director of religious publishing at Doubleday for six years.
Cahill's book, A Saint on Death Row: The Story of Dominique Green, represented a departure from the Hinges of History series.
It was both the story of Dominique Green, a young man from Houston who was on death row in Texas, and of the effect that knowing him had on Cahill.
Cahill first heard about Green from Judge Sheila Murphy who was working on the appeal of the case.
[6] Green made a final statement before his execution: There was a lot of people that got me to this point and I can't thank them all.