After his doctorate and his habilitation with Andreas Kraus with the work Studien zum Staatshaushalt Bayerns in der zweiten Hälfte des 15.
From 1989 until his retirement in 2002, Ziegler taught Bavarian regional history with a special focus on modern times at the Institute for Bavarian History [de] of the Ludwig-Maximilians-University of Munich as successor to Andreas Kraus.
Since 1994, Ziegler has been a full member of the Bavarian Academy of Sciences and the Swabian Research Foundation [de].
The focus of his academic work is the history of the State, especially of Bavaria and southern Germany, in the late Middle Ages and early modern times.
He has also published several works on the contemporary history of Bavaria in the 20th century, especially on the period of National Socialism and displacement.