The resolution, co-sponsored by 103 countries, was approved by consensus, without a vote.
It received almost as many co-sponsors as a broader measure adopted in November 2005 which made January 27 the International Day of Commemoration for victims of the Holocaust.
Iran disassociated itself from the US-drafted resolution and called it a political exercise.
Iran is not mentioned by name in the resolution but it is clearly a response to the Tehran conference convened in December by President Mahmoud Ahmadinejad.
Many speakers at the event expressed doubt about the Nazis' mass extermination of Jews.
|"We must strengthen our resolve to prevent such atrocities, whenever and wherever they might occur."|
Sheikha Haya Rashed al-Khalifa, UN General Assembly president
Hossein Gharibi, an Iranian envoy to the United Nations, told the assembly: "In our view there is no justification for genocide of any kind, nor can there be any justification for the attempt made by some - particularly by the Israeli regime - to exploit the past crimes as a pretext to commit new genocide and crimes."
In response, Dan Gillerman, Israel's ambassador to the UN, said: "While the nations of the world gather here to affirm the historicity of the Holocaust with the intent of never again allowing genocide, a member of this assembly is acquiring the capabilities to carry out its own."
"The president of Iran is in fact saying, 'There really was no Holocaust, but just in case, we shall finish the job,'" he added.
Up to 1.5 million prisoners, most of them Jews, are killed in the Auschwitz extermination camp alone.
Six million Jews and millions of other people including Poles, homosexuals, Russians and Gypsies are said to be murdered by the Nazis and their allies during the war.
Sheikha Haya Rashed al-Khalifa of Bahrain, the General Assembly president, told the 192 members that the resolution showed "we must strengthen our resolve to prevent such atrocities, whenever and wherever they might occur."