Pressac was originally a Holocaust denier who, with Robert Faurisson, attempted to disprove what he considered historically inaccurate depictions of the concentration camps Auschwitz and Birkenau as extermination camps.
Upon visiting Auschwitz in 1979, however, Pressac was able to view first-hand the extensive archive of construction documents which had survived due to being located in the construction office rather than the administrative offices. These convinced him that his former views were in error, an event he describes in the postface of Auschwitz: Technique and operation of the gas chambers, saying that he "nearly did away with myself one evening in October 1979 in the main camp, the Stammlager, overwhelmed by the evidence and by despair". He published his conclusions along with much of the underlying evidence in his 1989 book, Auschwitz: Technique and operation of the gas chambers.  In his 1993 Les Crématoires d'Auschwitz,  he further delineated the operation of the crematoria at Auschwitz, and their integration into the larger Nazi program to eradicate the Jews of Europe. Pressac estimates that between 631,000 and 711,000 were killed at Auschwitz.
- Pressac, Jean-Claude (1989). "Postface by the author". Auschwitz: Technique and operation of the gas chambers. New York: The Beate Klarsfeld Foundation. pp. 537–564. Retrieved 2006-01-31.
His position with respect to the extermination of the Jews at Birkenau and the personal experiences that led him to undertake this study
- Pressac, Jean-Claude (1989). Auschwitz: Technique and operation of the gas chambers. New York: The Beate Klarsfeld Foundation. Retrieved 2006-01-31.
- Pressac, Jean-Claude (1998-09-01) . Les crématoires d'Auschwitz (in French). CNRS Éditions. ISBN 2-271-05093-6.
- Pressac, Jean-Claude. Die Krematorien von Auschwitz. Die Technik des Massenmordes. p. 202.
- Jean-Claude Pressac. Les carences et incohérences du Rapport Leuchter (Deficiencies and incoherence of the "Leuchter" Report, Jour J., la lettre télégraphique juive, December 12, 1988
- Jean-Claude Pressac, Serge Klarsfeld. THE STRUTHOF ALBUM. Study of the gassing at Natzweiler-Struthof of 86 Jews whose bodies were to constitute a collection of skeletons. A photographic document. New York : Beate Klarsfeld Foundation, 1985