In 2000, he received his doctorate in Ancient History from the University of Heidelberg, Germany for a dissertation titled "Apuleius und die Räuber.
Riess was "Wissenschaftlicher Angestellter" (roughly equivalent to Assistant Professor) in the Seminar für Alte Geschichte und Epigraphik of the University of Heidelberg from 1999 through 2003.
During the academic year 2002/03, Riess held a Feodor Lynen-Fellowship from the Alexander von Humboldt-Foundation, which enabled him to teach and do research at Emory University, Atlanta, Georgia.
In 2004, Riess joined the faculty in the Department of Classics at the University of North Carolina at Chapel Hill.
After a research stint at the Harvard Center for Hellenic Studies at Washington, DC (2007/08), Riess earned the Habilitation at the University of Augsburg, Germany in 2008 for a thesis titled The Social Drama of Violence: A Cultural History of Interpersonal Violence in Fourth-Century BCE Athens.