He did parish work for seven years in Brackwede and was appointed prefect of the Collegium Leonianum, Paderborn, in 1959. At the same time he completed his doctoral thesis and was an assistant professor of theology in Bochum and later dean of the Hochstift Paderborn pastoral region.
On 12 March 1968 was appointed titular Bishop of Vicus Pacati and Auxiliary of Paderborn, receiving episcopal ordination on 1 May. On 4 April 1974 he was promoted to Archbishop of Paderborn. In 1990 he became Chairman of the Administrative Committee of the Association of German Dioceses.
Created and proclaimed Cardinal by John Paul II in the consistory of 21 February 2001. Titular church St. Liborius.
Cardinal Johannes Joachim Degenhardt died on 25 July 2002.