 In 1953, he entered St. Charles Borromeo Seminary in Overbrook, from where he obtained Bachelor of Arts degree in 1958.On May 19, 1962, Cullen was ordained to the priesthood by Archbishop John Krol in the Basilica of Saints Peter and Paul.He then served as an assistant pastor at St. Maria Goretti Church in Hatfield for three years and then at St. Bartholomew Church in Philadelphia.