His father, Otto Ther, directed several educational institutions, including the Outward Bound schools in Baad and Berchtesgaden.

In 2002, he worked as junior professor for Polish and Ukrainian studies at the European University Viadrina in Frankfurt (Oder), where he published his habilitation on the political and social function of the opera house in the 19th century.

Ther gained recognition as an expert on the history of expulsion and displacement in Europe and publicly criticized the German Federation of Expellees, whose policies he described as not being aimed at reconciliation even after the end of the Cold War.

The federation's then president Erika Steinbach subsequently intervened by lodging a complaint with Ther's publishing house Vandenhoeck & Ruprecht.

The publisher released this letter to the public and described it as "brazen meddling"[3] Since 2010, Ther has been a tenured university professor for the history of East Central Europe at the Institute of Eastern European History at the University of Vienna, where he served as the institute's executive director from 2014 to 2018.