Deacon Birkenmaier was ordained on June 7, 2003, at the Cathedral Basilica of Saint Louis by then-Archbishop Justin F. Rigali. He was assigned to and assisted the pastor at St. Monica Parish in Creve Coeur. In 2016, he retired from active ministry but continued to assist with hospital, nursing home and homebound Communion ministry. He served his parish by presiding at baptisms, funerals, weddings and Communion services. He also was a member of the St. Vincent DePaul Society and served as a chaplain at St. Louis Lambert International Airport.

Deacon Birkenmaier is survived by his wife, Mary Jean Birkenmaier (nee Kiley), children, Gregory Birkenmaier and Julie Birkenmaier, and two grandchildren. He was a special education teacher for 30 years for St. Louis Public Schools and co-owned a newspaper route for the St. Louis Globe-Democrat.