He earned a master’s degree in History and History of Eastern Europe at the University of ELTE, Budapest. He gained the dr. univ. degree in History in 1979, he received his PhD (kandidátusi) degree in History in 1993. Karsai defended his habilitation thesis (‘venia legendi’) in 1999. In 2014 the Hungarian Academy of Sciences awarded him the Higher Doctorate (DSc) title.
He has been researching the history of the Hungarian Roma and Jewish Holocaust, the history of the Hungarian extrem right-wing movements, mainly the Arrow Cross Party.
He is the leader of the Yad Vashem Archives Hungarian Research Group from 1994. He was the chief historical adviser of the first Hungarian Holocaust exhibition, Bp., IX. Páva street 39. (2003-2006). Member of the advisory board of the EHRI (European Holocaust Research Infrastructure, 2010-2015).
He has been invited by several research institutes and universities in Israel and North-America as research fellow and visiting professor, including the Yad Vashem International Institute for Holocaust Studies, Jerusalem, United States Holocaust Memorial Museum, Washington, DC, Columbia University in the City of New York.
He is the author of 7 books and editor of several other volumes, as well as a number of scholarly articles.