Boris Kozjak was born on October 23, 1948 in Potok, Kutina. He finished primary and secondary school in Zagreb. Kozjak graduated from the Faculty of Humanities and Social Sciences, University of Zagreb, at the Department of Sociology in 1997, got his M.A. from the Faculty of Economics in Zagreb in 1999, and at the end of 2013 he received his Ph.D. at the Faculty of Humanities and Social Sciences in Zagreb.
He spent most of his life working in the Croatia Lottery. Kozjak participated in ten international scientific conferences and one scientific expert conference. From the academic year 2015/2016. he has been teaching the course The Sociology of Gambling at the Department of Sociology at the Centre for Croatian Studies, University of Zagreb. He is a longtime member of the Croatian Sociological Society.