MEPs have changed the European Parliament's rules to prevent the French far-right leader, Jean-Marie Le Pen, from presiding over the assembly.
They voted overwhelmingly to change a rule that says the oldest member chairs the inaugural session of the new parliament after a European election.
Mr Le Pen could have had that role come 14 July. But now it will fall to the outgoing assembly's president.
The 80-year-old has described the Nazi gas chambers as "a detail of history".
Mr Le Pen is running for re-election in the European Parliament elections on 4-7 June, as leader of the French National Front (FN).
The head of the conservative EPP, the largest bloc in the parliament, backed the initiative of the Socialists and Greens to stop Mr Le Pen chairing the assembly.
Mr Le Pen's claim about the Holocaust - first made in 1987 - provoked widespread outrage and landed him a fine of 1.2m francs (185,000 euros; $290,000).
Six million Jews died at the hands of the Nazis during World War II, along with hundreds of thousands of Roma (Gypsies), homosexuals, disabled people, political dissidents and Soviet prisoners of war.