After completing his studies, Joachim Zahn joins State Service and becomes a Government Council. After 1945, he first belongs to the Board of Management of the German Trust Board and is appointed to the Board of Management of Daimler-Benz AG in 1958 following an engagement with the Aschaffenburger Pulp Plants.
In addition to the central financial management, he assumes the role of Chairman of the Board of Management in 1965 until he is appointed Chairman of the Board of Management of Daimler-Benz AG in 1971. His most important entrepreneurial decisions are the separation from Auto Union, the designation of the Wörth plant as central truck assembly plant, the concentration of heavy-duty engine manufacture in Friedrichshafen, the cooperation with MAN which led to the founding of MTU and the takeover by the company of the sales organisation in the most important exporting countries. For Joachim Zahn, the overall responsibility of the entrepreneur has priority. He feels equally responsible to shareholders and employees. In the Zahn era, the sales revenues of Daimler-Benz AG increase from DM 2.9 billion to more than DM 27 billion in 1979. Equity capital grows from DM 180 million to DM 3.2 billion; retirement capital increased from DM 73 million to DM 3.2 billion. Joachim Zahn pursues the controlled expansion of capacity so that Daimler-Benz could live off the order books in the crisis years 1966/67 and 1974/75, and manage to avoid layoffs.