Much of Nikolaus’ research has explored Nazi terror, focusing on the regular legal system and extra-legal terror in concentration camps. His comprehensive history of the Nazi camps KL, published in 2015, won the Wolfson History Prize, the Mark Lynton History Prize, and the Jewish Quarterly-Wingate literary prize.
Nikolaus has a particular interest in public history and Holocaust education. He was a researcher for Deborah Lipstadt’s defence team in the 2000 High Court libel suit brought against her by Holocaust denier David Irving, and currently serves on the academic advisory boards of the UK Holocaust Memorial Foundation, as well as the concentration camp memorials Bergen-Belsen, Mauthausen, Sachsenhausen and Ravensbrück. He also curates a free educational website The Nazi Concentration Camps for students and teachers.