He has authored four books, Citizenship and Immigration in Postwar Britain,[1] Fire and Fury: the Allied Bombing of Germany 1942-1945,[2][3] Disobeying Hitler: German Resistance after Valkyrie.,[4] and War, Work and Want: How the OPEC Oil Crisis Caused Mass Migration and Revolution [5] Hansen was co-editor (with Matthew J. Gibney) of Immigration and Asylum: From 1900 to the Present.

[6] He is co-author (with Desmond King) of Sterilized by the State: Eugenics, Race and the Population Scare in 20th Century North America.

In 2018, sales of Fire and Fury surged upon the publication of Michael Wolff's best-selling book of the same title about the Presidency of Donald Trump.

The Guardian reported Hansen's reaction to the interest in his book about the consequences of war: "And we’re talking about that at a moment when we have this warmongering, unstable, deranged demagogue in the White House," he said.

"[11]Hansen was the Interim Director of the Munk School of Global Affairs for the period 1 June 2017 to 31 January 2020, succeeding Stephen Toope,[12] and Director of the Centre for European, Russian and Eurasian Studies at the Munk School from 2011 to 2022.