Upon completion of the college ROTC program at Washington and Lee University in 1984, Seidule became an officer in the United States Army. Seidule served for 36 years, starting as a tank platoon leader in Germany. His commands include a cavalry unit in the 82nd Airborne Division during the Gulf War, as well as 3rd Battalion, 81st Armor Regiment. His staff positions included crisis planning for NATO in Kosovo and North Macedonia.