Most Reverend John W. Flesey is a Jersey City native. He attended Saint Peter's Preparatory School and College. He was ordained in 1969 in Sacred Heart Cathedral after studying for the priesthood at Immaculate Conception Seminary. 

His first assignment was to St. Bernard of Clairvaux Parish, Plainfield, where he served for 14 years. While there, he completed an M.A. in pastoral counseling from Iona College, New York, and was involved in a program for the renewal of priests.

In 1983, Bishop Flesey studied for a licentiate in spiritual theology from Gregorian University, Rome. He received his degree in 1985. He returned to serve at Immaculate Conception Seminary.

In 1990, Bishop Flesey defended his thesis for his doctorate in theology from the University of Saint Thomas, Rome. In December 1996, he was elevated to the rank of Prelate of Honor and given the title of Monsignor.

From 1995-2000, Bishop Flesey served as rector of the seminary before taking a sabbatical year in Italy. He returned to the seminary, and in September 2002 was named Director of the Office of Continuing Formation of Priests.

On June 1, 2004, he became pastor of Most Blessed Sacrament Church in Franklin Lakes, New Jersey. On August 4, 2004 he was named Titular Bishop of Allegheny, Auxiliary Bishop of Newark and Regional Bishop of Bergen County.

On July 1, 2018, Bishop Flesey became the Pastor Emeritus of Most Blessed Sacrament Church. He remains in residence at MBS while he continues to serve at Regional Bishop of Bergen County.