After his ordination to the Catholic priesthood, Harrington was assigned to Niagara University. He served as an associate professor in Religious Studies, and later Director of Student Activities and Executive Vice President before being named the institution’s 22nd President. He was 38 years of age at the time, the youngest President in the history of the school. During his tenure at St. John's, he oversaw a transformation of the focus of the school from that of a commuter college, geared to the local Catholic population, to one which draws its student body from across the nation.[1]
On May 3, 2013, Father Harrington announced that he would retire as President of St. John's University, effective July 31, 2013.[3] Harrington's retirement announcement came in the middle of an investigation of corruption,[4] in which he was widely criticized for accepting expensive gifts and trips during his presidency and for failing to supervise a dean of the university who was accused of embezzling a huge sum of money, in a scandal which resulted in that dean's suicide. He was succeeded by the Rev. Joseph L. Levesque, C.M., serving as Interim President.[1]