Ratajczak was born in Opole, Upper Silesia, Poland. His father, Cyryl, moved from Greater Poland to Opole after finishing Law studies. His mother, Alina Czuchryj, arrived from Khodoriv. Dariusz Ratajczak finished Opole high school and enrolled to Adam Mickiewicz University in Poznań. From 1988 Ratajczak was working in a higher education institution in Opole, later changed to University of Opole, as a history lecturer until 1999. In that year he was dismissed following the controversy about his book Dangerous Topics, in which he asserted that the gas chambers at Auschwitz were used only to delouse the prisoners. He had also published articles in right-wing magazines Myśl Polska and Najwyższy Czas!.
According to Ruth E. Gruber report, Dariusz Ratajczak, in his book Tematy Niebezpieczne ("Dangerous Topics"), appeared to agree with Holocaust deniers, who claimed that for technical reasons it was not possible to kill millions of people in the Nazi gas chambers, that Zyklon B gas was used only for disinfecting, that there was no Nazi plan for the systematic murder of Jews and that a majority of Holocaust scholars "are adherents of a religion of the Holocaust". Rajtaczak would defend himself claiming that he only quoted the Holocaust deniers' claims to illustrate their point of view, but did not endorse them.
Ratajczak's book triggered widespread public criticism and drew protests from numerous sources, including the director of the museum at the former Auschwitz death camp, senator Władysław Bartoszewski, the mainstream Polish academic community and the bishop of Lublin.
The University of Opole suspended Dariusz Ratajczak from teaching in 1999. In the same year he was taken to court, as denying the existence of the Holocaust was a criminal offence in Poland. In December 1999 the local court in Opole found Ratajczak guilty of breaching the Institute of National Remembrance law that outlawed the denial of crimes against humanity committed by the Nazi or communist regimes in Poland, but that his crime had caused "negligible harm to society". The reason for the low sentence was that Ratajczak's self-published book had only 230 copies and that in the second edition and in his public appearances he criticized the Holocaust denial.
The verdict was criticized by some, including the former victims of Nazi crimes, as too lenient. Ratajczak was defended by one of the leaders of the League of Polish Families party Ryszard Bender, who during a Radio Maria broadcast denied the fact that Auschwitz was a death camp, which caused another scandal in Poland.
In the end Dariusz Ratajczak was fired from the University of Opole in 2000 and banned from teaching at other universities for three years. During this time he worked as storeman.
In 2000 he became a European Associate of the Adelaide Institute, Australia.
Ratajczak remained defiant and denied all charges, appealing for an outright acquittal; his critics also appealed demanding a harsher sentence, including a prison term. Eventually after a series of appeals the verdict was upheld, while the case was dismissed in 2002.
A scandal surrounding the Ratajczak’s book, whose publication reputedly represents the first serious case of Holocaust denial in Poland (although there have been other similar cases).
Ratajczak revised his book in 2005, attributing the claims regarding Zyklon B to historical revisionists.
Ratajczak believed that charge of anti-Semitism had become a blunt and brutal weapon, which the "establishment" uses ruthlessly against free-thinking men:
What hurts me most is that I found myself in a group of historians who have been muzzled. After all, please see: from 1945 until now the number of Jews murdered in Auschwitz-Birkenau has dropped from six million to less than one million. It's official data. Indeed, even if they had killed one man, that would be a tragedy. But how is it that some historians may legitimately question the numbers of the Holocaust while others can not? How is it that some people can reduce the six million to less than a million and nothing bad has happened to them? How is it that some people are not allowed to examine this subject and even be wrong, while other historians are allowed all this?
Dariusz Ratajczak was found dead in a car parked near the shopping centre in Opole on 11 June 2010. The body was lying in the car for nearly two weeks and was in an advanced state of decay. The autopsy discovered that fatal alcohol poisoning was the cause of Ratajczak's death.
In 2002 Ratajczak was considered as a candidate of the League of Polish Families for the Opole's voivodeship sejmik, but after his candidature caused controversy he resigned from running for the office.Polacy na Wileńszczyźnie 1939-1944 (Opole 1990)
Świadectwo księdza Wojaczka (Opole 1994)
Krajowa Armia Podziemna w powiecie prudnickim 1949-1952 (współautor, Opole-Gliwice 1996)
Tematy niebezpieczne (Opole 1999)
Tematy jeszcze bardziej niebezpieczne (Kociaty, New York, 2001)
Inkwizycja po polsku, czyli sprawa dr Dariusza Ratajczaka (Poznań 2003)
Prawda ponad wszystko (Opole 2004)
Spowiedź "antysemity" (Opole 2005)