The son of a Lutheran minister, Ottomar Tietjen attended California Concordia College in Oakland, California, and then graduated from Concordia Seminary in St. Louis. Like his father, he was ordained a Lutheran minister, and accepted a call to Yuma, Arizona, as pastor of Calvary Lutheran Church. He was commissioned a U.S. Army chaplain during World War II, serving in the Pacific Theater of Operations, and continuing in military service as a chaplain until his retirement in 1967 as an Army colonel. In retirement he pastored churches in Burbank, Alameda, and Glenoaks, California, during pastoral vacancies, and then accepted a call to be permanent pastor in East Valley. Further, in retirement from full-time ministry he served as chaplain to patients in four veterans hospitals in the Los Angeles area.