Since 2009 he has been an extraordinary professor at the Bergische Universität Wuppertal and since 2011 he has been head of the Archive of Liberalism of the Friedrich Naumann Foundation for Freedom in Gummersbach.

Between 1992 and 1995 he was a fellow of the graduate program "Medieval and Modern Statehood (10th-19th Century)" at the Justus Liebig University Gießen and from 1993 to 1995 he was a research assistant at the "Research Center Georg Büchner – Literature and History of the Vormärz" at the University of Marburg.

In 1995 he went to the Bergische Universität Wuppertal as a research assistant to Hartwig Brandt, where he habilitated in 2003 on German constitutional historiography in the 20th century.

As of April 2011, he has been appointed head of the Archive of Liberalism of the Friedrich Naumann Foundation for Freedom in Gummersbach, succeeding Monika Faßbender.

In 1995, Grothe won the Wilhelm Liebknecht Prize of the university town of Gießen for his dissertation.