Diers studied art history, literature, and philosophy in Münster and Hamburg, where he received his doctorate with a thesis on Aby Warburg.
From 1990 to 1992 he was assistant professor at the Kulturwissenschaftliches Institut, Essen, and subsequently at the Department of Art History, Universität Hamburg, in the joint research project "Politische Ikonographie".
In 1994 he became lecturer at the Universität Jena, in 1999 at the Humboldt-Universität zu Berlin, where he also served as Director of the Department of Art History (2000–2002).
In 2004, Diers was appointed professor of art history and visual studies at the Hochschule für bildende Künste Hamburg, where he retired in 2017.
He currently serves as co-editor of the "Studienausgabe Aby Warburg, Gesammelte Schriften" (De Gruyter, since 1998) and from 2004 to 2016 the monograph series "Humboldt-Schriften zur Kunst- und Bildgeschichte" (Gebr.