He then served as the Senior Historian in the Holocaust Exhibition Project Office at the Imperial War Museum in London in 1998–2000.
He was the Koerner visiting fellow and lecturer at the Oxford Centre for Hebrew and Jewish Studies, and Pearl Resnick fellow at the Center for Advanced Holocaust Studies at the US Holocaust Memorial Museum.
Paulsson's book, Secret City, is a social history of the Jews who escaped from the Warsaw ghetto and tried to survive, living illegally "on the Aryan side".
In its original form as his doctoral thesis, it was awarded the Franklin Prize in Contemporary History (1998).
The English edition was awarded the biennial PSA/Orbis (now Kulczycki Prize) in 2004, and the Polish edition, Utajone Miasto: Żydzi po "aryjskiej" stronie Warszawy 1940-1945 (Znak, 2007) was awarded the inaugural Moczarski Prize (pl) for the 2009 best book in history.