János Köllõ studied economics at the Budapest (then Karl Marx) University in 1972-77. He has a doctoral degree in sociology (1980) and a "candidate's degree" (Ph.D.) in economics (1990). He is a full-time researcher at the Institute of Economics of the Hungarian Academy of Sciences (1977-92, 1994-). Served as a visiting researcher in Collegium Budapest Institute for Advanced Study (1993-94), and the William Davidson Institute, Ann Arbor (2003).
He has been engaged in the analysis of labor markets, industrial relations and the transformation of Central and East European labor markets in the post-communist period.
He joined IZA as a Research Fellow in October 2000.