Security for the trial is being handled by anti-terrorist police because of fears neo-Nazis will attempt to hijack the proceedings.
A security zone has been thrown around the state court, manhole covers welded shut and bomb sniffing dogs deployed.
Irving has received more than 200 letters a week supporting his views that the systematic murder of six million Jews in gas chambers did not take place during the Second World War.
He has since indicated that he has "revised" his views about the existence of gas chambers. He does not consider himself guilty, but will admit the charge because he "has no choice".
Irving, 67, was arrested last November after a routine check on a highway in Austria on a 1989 warrant.
The warrant was issued by a Vienna court against Irving for having allegedly denied at meetings in Austria around 1989 that the Nazi regime used gas chambers in concentration camps.
Denying the Holocaust is illegal in Austria, as it is in Germany.