In 1979 he completed his studies with the first state examination for teaching at grammar schools in the subjects of history and Latin.
Instead of teaching, Gestrich became a research assistant to a DFG project on the social history of childhood, youth and family at the Institute of Education at the University of Tübingen.
From 1992 to 1997 Gestrich held substitute professorships in Würzburg, Karlsruhe and Trier.
In September 2006 he became director of the German Historical Institute in London.
In August 2018, he was awarded the President's Medal of the British Academy "for his contribution to the study of German and Continental European History".