Thissen served in the German Bishops' Conference as the bishop responsible for the Misereor aid agency from 2000 to 2014.[1] He was named Archbishop of Hamburg by Pope John Paul II on 22 November 2002; he was installed on 25 January 2003.[2][4] He is credited with the development of the young diocese. One of his initiatives was to call people to meeting each other in pastoral conversations titled Salz im Norden. He also worked for a restoration of the St. Mary's Cathedral, including new features. He initiated the process to beatify the Lübeck martyrs.[1][7] Thissen resigned at age 75, which was granted by Pope Francis on 21 March 2014,[1][8] and subsequently became archbishop emeritus of Hamburg.[9]
Thissen died in Hamburg on 15 April 2025, at the age of 86.[1][5][7]