From 1966 to 1982 he worked for Metallgesellschaft AG, Frankfurt am Main. Within the Metallgesellschaft Group, he was CEO for the subsidiary "Erzgesellschaft mbH" (from 1968), and from 1971 to 1982 Chief technical officer of "Synthomer Chemie GmbH", another subsidiary.
He was co-president of the German-Japanese Cooperation Council for High-technology and Environmental Technology DJR in Bonn. Snce 1995 he is honorary professor at the University of Frankfurt and president of the German Parliamentary Union (Deutsche Parlamentarischen Gesellschaft) since 2006.
Riesenhuber is a member of several governing boards and advisory committees of German and foreign companies and institutes. He lives in Frankfurt-Unterliederbach, is married and has four children.
Riesenhuber became a member of the Christian Democratic Union (CDU) in 1961. Between 1965 and 1969 he was head of the youth organization of CDU (Junge Union) in Hessen. He was chairman of CDU Frankfurt from 1973 to 1978. In 1979 he was elected as a chairman of CDU district Untermain (now FrankfurtRheinMain).
In 2009 he became the 17th Alterspräsident (Father of the House) of the Bundestag due to his status as the oldest member of the legislature. He continued to hold this post in the following legislature. In 2017 he did not run for parliament again.
His personal brand is his Bow tie. He always wears such a tie. In his political campaigns for the Bundestag he used a poster showing only a bow tie in the national colours of Germany: Black, red and gold. Neither his name nor his party was mentioned but everybody in his constituency recognized Riesenhuber.
Speaker: Marieluise Beck-Oberdorf, Petra Kelly, Otto Schily until 3 April 1984; Annemarie Borgmann, Waltraud Schoppe, Antje Vollmer until 30./31. January 1985;
Sabine Bard, Hannegret Hönes, Christian Schmidt until 1 February 1986; Annemarie Borgmann, Hannegret Hönes, Ludger Volmer until 18 July 1986); Willi Hoss (8 September 1986)
Speaker: Thomas Ebermann, Bärbel Rust, Waltraud Schoppe until 26 January 1988; Helmut Lippelt, Regula Schmidt-Bott, Christa Vennegerts until 30 January 1989, Helmut Lippelt, Jutta Oesterle-Schwerin, Antje Vollmer until 15 January 1990; Willi Hoss, Waltraud Schoppe (until 21 June 1990), Marianne Birthler (from 4 October 1990), Antje Vollmer