Deacon Shannon was ordained on June 9, 2001, at the Cathedral Basilica of Saint Louis by then-Archbishop Justin F. Rigali. He was assigned to and assisted the pastor at All Souls Parish in Overland, where he served as a deacon for five years. In 2006, Deacon Shannon retired from active ministry at All Souls Parish but continued to assist part-time at Holy Spirit and St. Ann parishes. He served his parishes by presiding at baptisms, funerals, weddings and Communion services. Deacon Shannon also served as a spiritual director.

Deacon Shannon is survived by his wife, Ruth Ann Shannon; children, David (Cheryl), Christie (Dave) and Katy (Paul); and many grandchildren. He served as a Christian Brother from 1949-67 and was a teacher for 42 years, including at the University of Iowa and St. Louis University High School.