Britain will not take part in the anniversary event later this month marking ten years since the UN's controversial Durban conference.
The Prime Minister, following in the footsteps of Australia, Canada and the United States, said he felt it would be wrong to commemorate an event associated with "open displays of unpleasant and deplorable antisemitism".
The 2001 World Conference on Racism, held in Durban, South Africa, was criticised after it descended into a forum to attack Israel.
The then Palestinian leader Yasir Arafat used one session publicly to denounce Israel and there was an attempt to reintroduce the "Zionism equals racism" UN resolution of 1975.
A review conference in Geneva two years ago attracted a similar outcry after Iranian President Mahmoud Ahmadinejad was invited to make the opening-day address and accused Israel of being racist.
The UK delegation walked out of Ahmadinejad's speech but faced criticism for not taking a strong enough stand and Mr Cameron was determined not to repeat that this year.
He said that after "careful consideration", he had decided Britain should not attend.
"No one should be in any doubt: this government is 100 per cent committed to tackling racism both at home and abroad," he said. "But those aims cannot be met by accepting this invitation."
He added that the displays of antisemitism at the first conference should be condemned, not commemorated.
Last year the UK voted against the resolution establishing the conference "in light of" the events of 2009, but until now the government had refused to say if UK representatives would take part, despite calls from the Jewish community and human rights group
Vivian Wineman, president of the Board of Deputies, said he was delighted with Mr Cameron's decision. "It is farcical that a conference which may again be addressed by President Ahmadinajad of Iran can have any pretentions to be taken seriously on the matter of human rights or any other topic," he said.