János Köllő is a Senior Research Fellow at the Institute of Economics (IE), Budapest, and director of its Databank. He has been affiliated with IE since graduation, with interruptions in Collegium Budapest - Institute of Advanced Study (1993-94) and University of Michigan Business School (2003). He is a Research Fellow at IZA, Bonn, a member of the Academia Europaea, and the GLO Country Lead Hungary.

He has written widely on unemployment in Central and Eastern Europe, demand for human capital, industrial relations, and ethnic and regional inequalities. He consulted in the elaboration of post-communist Hungary's labor market institutions and has been doing contract work for different Hungarian governmental agencies.

He has participated in numerous international research projects sponsored by the Commission of the European Union, ILO, EBRD, and the World Bank