Kasahara retired from the United Nations Conference Trade and Development (UNCTAD) secretariat at the end of May 2013, after having served for the organization nearly 25 years. During the professional career as an economist, he was almost always in the area of research and publication for the organization, such as the flagship publications, the Trade and Development Report, the Economic Development in Africa Report, etc.
His professional interests cover a wide range of international political economy: development economics, trade and development, international trade regimes, trade development diplomacy, the role of the state (development policy), regional integration, industrialization, East Asian development (the Flying Geese paradigm), Africa, Least Developed Countries (LDCs), foreign direct investment (FDI), global value chains, institutional history of UNCTAD, etc.
He has frequently given lectures to graduate student groups visiting the UN as well as at various locations (SOAS in London, IDEAS in Makugari, HUFS in Seoul, GSID in Nagoya, etc.).