Her doctoral thesis, in which she adduced evidence of a history of antisemitism and support for European fascism among Quebec nationalists of the 1930s, was controversial long before it was published.

(Different versions of this incident appear in Sara Scott, "The Lonely Passion of Esther Delisle", Elm Street, April 1998, p. 97, and Sheli Teitelbaum, "Quebec and French Nazis", The Canadian Jewish News, December 15, 1994, reprinted from The Jerusalem Report.)

A 2002 documentary film by Eric R. Scott titled Je me souviens recounts Delisle's story using rare archival footage with speeches and commentaries by some of Quebec's leading nationalist figures of the time.

She attacks as myth the beliefs put forward by historians such as Lionel Groulx that the Québécois are a racially and ethnically homogeneous group of pure descent from French Catholics who immigrated to New France.

In 1998, Delisle published, Myths, Memories and Lies, an account of how some members of Quebec's elite, nationalist and federalist, supported the French Nazi collaborator military officer Philippe Pétain and his Vichy government within German-occupied France during World War II and also helped bring other French collaborators to safety in Quebec after the conflict ended in Europe.