Duffy then served as assistant pastor at the Church of Our Lady of Grace (Hoboken, New Jersey), professor of literature and languages at Seton Hall University, and instructor in Church history at the Newark seminary.Duffy was named a domestic prelate, and served as chancellor and vicar general for the diocese.
Duffy held various positions within the Catholic Church: assistant pastor at the Church of Our Lady of Grace, professor of literature and languages at Seton Hall University, and instructor in Church history at the Newark seminary. He was also named a domestic prelate and served as chancellor and vicar general for the diocese.