Mensing was born in Hamelin and, after graduating from the local Gymnasium, completed an apprenticeship as a butcher. After passing his master craftsman's examination, he took over his father's business in Hamelin in 1924 and was a member of the board of the Northwest German Craftsmen's Association. During the Weimar Republic, Mensing was politically active as a member of the conservative Economic Party, also known as the Reich Party of the German Middle Class (German: Reichspartei des deutschen Mittelstandes). He represented the party as a deputy in the provincial parliament of the Province of Hanover from 1925 to 1933. After the Nazi seizure of power, all other parties were outlawed. Throughout the duration of Nazi Germany from 1933 to 1945, Mensing was not politically active and held no political office.
After the fall of the Nazi regime in 1945, Mensing reentered politics, and served for a time on the Hamelin city council. He became chairman of the German Butchers' Association and a member of the presidium of the Central Association of German Crafts, as well as holding other positions in craft organizations. He joined the Christian Democratic Union of Germany (CDU) and was elected to the first West German Bundestag in 1949. He was reelected in 1953 and 1957 and served until 1961, entering parliament in each election via the Lower Saxonystate list of the CDU. Mensing was a member of the Committee on Food, Agriculture, and Forestry. He was also chairman of the supervisory board of the Volksbank Hameln (a cooperative bank), the main cooperative of the butchery trade. In 1968, he was honored by the German Agricultural Society for exceptional services to the German meat industry. Mensing died in Hamelin in November 1978.
Herbst, Ludolf; Jahn, Bruno (2002). Vierhaus, Rudolf (ed.). Biographisches Handbuch der Mitglieder des Deutschen Bundestages. 1949–2002 [Biographical Handbook of the Members of the German Bundestag. 1949–2002] (in German). München: De Gruyter - De Gruyter Saur. p. 1715. ISBN978-3-11-184511-1.
Dorls (from 13 December 1950 WAV-Gast, from 17 January 1951 WAV, from 26 September 1951 Non-attached, am 23 October 1952 Mandatsaberkennung)
Frommhold (from 7 September 1949 Nationale Rechte, from 5 October 1950 Non-attached (DRP), from 26 March 1952 DP-Gast, from 11 February 1953 Non-attached)
Miessner (from 5 October 1950 FDP-Gast, from 20 December 1950 FDP)
Rößler (from 15 September 1949 Nationale Rechte, from 6 September 1950 Non-attached, from 13 December 1950 WAV-Gast, from 17 January 1951 WAV, from 26 September 1951 Non-attached, until 21 February 1952)
Thadden (from 15 September 1949 Nationale Rechte; 1950 DRP, from 20 April 1950 Non-attached)
Ott (Non-attached, from 4 May 1950 WAV-Gast, from 13 October 1950 BHE/DG, from 21 March 1952 Non-attached, from 26 March 1952 DP/DPB-Gast, from 26 June 1952 Non-attached)
Berg (from 27 June 1955, from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Blank (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Blücher (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Euler (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Fassbender (from 18 November 1955 DP, from 14 March 1957 DP/FVP)
Hübner (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Manteuffel (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Neumayer (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Preiß (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Preusker (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Schäfer (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Schneider (from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Bender (from 12 July 1955 Non-attached, from 14 July 1955 Group Kraft/Oberländer, from 15 July 1955 Guest of CDU/CSU-Fraktion, from 20 March 1956 CDU/CSU)
Eckhardt (from 12 July 1955 Non-attached, from 14 July 1955 Group Kraft/Oberländer, from 15 July 1955 Guest of CDU/CSU-Fraktion, from 20 March 1956 CDU/CSU)
Finck (from 12 July 1955 Non-attached, from 14 July 1955 Group Kraft/Oberländer, from 15 July 1955 Guest of CDU/CSU-Fraktion, from 20 March 1956 CDU/CSU)
Haasler (from 12 July 1955 Non-attached, from 14 July 1955 Group Kraft/Oberländer, from 15 July 1955 Guest of CDU/CSU-Fraktion, from 20 March 1956 CDU/CSU)
Körner (from 12 July 1955 Non-attached, from 14 July 1955 FDP, from 23 February 1956 Non-attached, from 15 March 1956 Demokratische Arbeitsgemeinschaft (DA), from 26 June 1956 FVP, from 14 March 1957 DP/FVP)
Kraft (from 12 July 1955 Non-attached, from 14 July 1955 Group Kraft/Oberländer, from 15 July 1955 Guest of CDU/CSU-Fraktion, from 20 March 1956 CDU/CSU)
Oberländer (from 12 July 1955 Non-attached, from 14 July 1955 Group Kraft/Oberländer, from 15 July 1955 Guest of CDU/CSU-Fraktion, from 20 March 1956 CDU/CSU)
Samwer (from 15 October 1953, from 12 July 1955 Non-attached, from 14 July 1955 Group Kraft/Oberländer, from 15 July 1955 Guest of CDU/CSU-Fraktion, from 20 March 1956 CDU/CSU)