Father Mann began his career as a priest teaching at Purcell High School in Cincinnati. He then taught and ministered at Marianist schools and parishes in Long Island, N.Y., Alameda, CA, and with his longest tenure at Holy Family Parish in Honolulu, near Pearl Harbor. In addition, he was an adjunct professor at Chaminade University of Honolulu. Father Mann concluded his active life teaching at Chaminade Prep in West Hills, CA.