From 1993 to 1995 Brendle received a doctoral scholarship from the Konrad-Adenauer-Stiftung and was at the same time research fellow, from 1997 to 1998 as scientific assistant, at the History Department of the University of Tübingen.
He 2008 he received his habilitation at the University of Tübingen with the thesis Der Erzkanzler im Religionskrieg.
Archbishop Anselm Casimir Wambold von Umstadt, Kurmainz and the Empire 1629 to 1647.
Brendle was an associate member of the Tübingen Research Training Group Ars and Scientia in the Middle Ages and Early Modern Times from 1995 to 2005.
Since 1998 he has been a member of the Scientific Advisory Board of the Society for the Publication of the Corpus Catholicorum and from 2011 to 2015 he is sub-project leader of the Collaborative Research Centre 923 Threatened Orders.