Klemm was a member of the Academy of Sciences Leopoldina (Deutsche Akademie der Naturforscher Leopoldina) in Halle, Germany; the Bavarian Academy of Sciences and Humanities (Bayerische Akademie der Wissenschaften) in Munich, Germany;
the Göttingen Academy of Sciences (Akademie der Wissenschaften zu Göttingen) in Göttingen, Germany; and 
the Rhine-Westphalian Academy of Sciences in Düsseldorf, Germany.
Klemm was co-editor of Zeitschrift für anorganische und allgemeine Chemie (the journal for inorganic and general chemistry) from 1939 to 1965.
From 1945 onwards, his central tasks were to reestablish teaching and research in Kiel (1947-1951) and in Münster (1951-) and to help reconstruct chemical institutions at the national and international levels.
Wilhelm Klemm was an influential science organizer. He became the second president of the Gesellschaft Deutscher Chemiker (1952-1953), working to foster communication between chemists in different zones of post-war Germany. 
In the 1950s and 1960s, he worked to build communication and cohesion between scientists in the GDR and the Federal Republic. 
As president of the GDCh he participated in the founding  of the Chemical Society of the GDR, formally created on 11 May 1953.
Wilhelm Klemm campaigned for international exchange in the sciences. From 1965 to 1967 he was President of the International Union of Pure and Applied Chemistry (IUPAC). 
He was the first German scientist to fill such a high international position after World War II.
In 1966 he became the secretary-treasurer of the recently formed Committee on Data for Science and Technology (CODATA) of the International Council of Scientific Unions (ICSU), whose purpose was to encourage the use of international standards of scientific nomenclature, symbols, constants, and data sets. He served on the committee from 1968 to 1975, also holding the position of vice-president.