Born in Offenbach am Main, Hammerstein is the son of the elementary school teacher August Hammerstein. He attended the Heinrich-von-Gagern-Gymnasium in Frankfurt and passed his Abitur there in 1949. He then studied economics and philosophy, later history, philosophy and English literature at the Goethe University Frankfurt and the Ludwig Maximilian University of Munich. In 1956 he was appointed a Doctor in Frankfurt by Otto Vossler, then became a research assistant and from 1960 assistant at the Department of History. In 1968 he habilitated and obtained the for Medieval and Modern History. In 1971 Hammerstein was appointed professor in the course of the new Hessian Higher Education Act and in 1973 he was appointed to a newly established Extraordinary Office for Early Modern History at Frankfurt University. He was disenfranchised in 1999. His brother Reinhold was professor for musicology at the Heidelberg University, his brother Gerhard honorary professor for criminal law at the University of Freiburg. In 1999 Hammerstein published a book on the history of the Deutsche Forschungsgemeinschaft during the Weimar Republic and the Third Reich. Ernst Klee called this book an "attempt at a clean slate", since Hammerstein described the work of the Nazi psychiatrist Robert Ritter as "general medical research", although he had divided the work of the Nazi psychiatrist into "full Gypsies", "Gypsy half-breeds" and "non-Gypsies" in his "expert opinions" in a racist manner.
1988 to 2006: German representative and vice chairman of the International Commission of the History of Universities in the International Association of Historians.
Publications
Jus und Historie. Ein Beitrag zur Geschichte des historischen Denkens an deutschen Universitäten im späten 17. und im 18. Jahrhundert.Vandenhoeck & Ruprecht, Göttingen 1972, .
Aufklärung und katholisches Reich. Untersuchungen zur Universitätsreform und Politik katholischer Territorien des Heiligen Römischen Reiches deutscher Nation im 18. Jahrhundert.. Duncker & Humblot, Berlin 1977,.
* Volume 3: Ihre Geschichte in den Präsidentenberichten 1972–2013, Wallstein Verlag, Göttingen, 2014.
Antisemitismus und deutsche Universitäten. 1871–1933. Campus, Frankfurt among others 1995,.
.
* as publisher with : Vol 1: Von der Renaissance und der Reformation bis zum Ende der Glaubenskämpfe. Beck, Munich 1996, ;
* as publisher with : Vol. 2: 18. Jahrhundert. Vom späten 17. Jahrhundert bis zur Neuordnung Deutschlands um 1800. Beck, Munich 2005,.
Die Deutsche Forschungsgemeinschaft in der Weimarer Republik und im Dritten Reich: Wissenschaftspolitik in Republik und Diktatur: 1920-1945. Beck, Munich 1999, ;
* Ingo Haar: Rezension in H-Soz-u-Kult 25 September 2000 .
Res publica litteraria. Ausgewählte Aufsätze zur frühneuzeitlichen Bildungs-, Wissenschafts- und Universitätsgeschichte. Edited by Ulrich Muhlack and Gerrit Walther. Duncker & Humblot, Berlin 2000,.
