Marchart studied philosophy at the University of Vienna, and also political theory and discourse analysis at the University of Essex under the supervision of Ernesto Laclau.

Marchart received his PhD in philosophy from the University of Vienna in 1999. In 2003, he earned a second PhD in English under the supervision of Ernesto Laclau, with a dissertation entitled "Politics and the Political: An Investigation into Post-Foundational Political Thought." Étienne Balibar and Simon Critchley were his other two examiners.

Between 2001 and 2006, Marchart worked as a research assistant at the Institute for Media Studies at the University of Basel. From July 2006 to 2012, he was a lecturer in the Department of Sociology at the University of Lucerne, with a fellowship funded by the Swiss National Science Foundation. Between 2012 and 2016, Marchart was a lecturer in Sociology at the Düsseldorf Art Academy. Since 2016, he has been a professor in the Department of Political Science at the University of Vienna, where he holds the Chair of Political Theory, succeeding Eva Kreisky.