On April 4, 1941, he was appointed Coadjutor Bishop of Speyer and Titular Bishop of Lebessus. He received his episcopal consecration on the following June 29 from Bishop Ludwig Sebastian, with Bishops Matthias Ehrenfried and Joseph Kolb serving as co-consecrators. Wendel succeeded Sebastian as Bishop of Speyer on May 20, 1943, being installed on June 4 of that same year. During World War II, he strongly defended the rights of the Church and humanity.[1] Wendel became known as the "Bishop of Peace" following the war because of his efforts to restore West Germany's good will[2]
Shortly after delivering his New Year's Eve sermon, Wendel died from a heart attack in Munich, at age 59.[2] He is buried in the metropolitancathedral of that same city.