David Irving said his views have changed since the speech at which he said there were no gas chambers in Auschwitz.
He was arrested and has been held since November when he returned to Austria to give a lecture to right-wing students, the BBC reports.
The 68-year-old was charged under an Austria law making it illegal to deny the Holocaust and faces 10 years in jail.
Austria is one of nine countries in Europe, as well as Israel, that have laws banning Holocaust denial.
Irving told the court he had changed since the speech, saying, "I'm not a Holocaust denier" and calling it "the Jewish tragedy of World War II."
Irving had with him a book he wrote called "Hitler's War," which argues against the Holocaust.
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