Zimbabwe has won approval to lead the UN body that promotes economic progress and environmental protection despite protests from some Western countries and human rights organisations.
UN officials said the Commission on Sustainable Development voted on Friday evening, while the US said the decision risked the commission's credibility.
The vote was 26-21, plus three abstentions, announced Luiz Alberto Figueiredo Machado, the vice chair of the commission.
The chair traditionally rotates among regions of the world and it is Africa's turn this year.
The continent has chosen Zimbabwe as its candidate, and the government has nominated Francis Nhema, the minister of environment and tourism, to chair the commission.
Several European nations have called Zimbabwe's candidacy inappropriate. The US said Zimbabwe would not be an effective leader of the group.
Dan Reifsnyder, the US representative to the commission, said: "We're very disappointed in the election of Zimbabwe as chair.
"We really think it calls into question the credibility of this organisation to have a representative from a country that has decimated its agriculture, that used to be the breadbasket of Africa and can't now feed itself."
Economic crisis
Zimbabwe is suffering its worst economic crisis since independence in 1980, with acute shortages of food, hard currency, petrol, medicines and most other basic goods.
Official inflation is running at about 2,200 per cent annually, the highest in the world.
Robert Mugabe, the president, an 83-year-old former anti-colonial rebel who has ruled Zimbabwe since independence from Britain, has acknowledged that police have used violent methods against opposition supporters and killed at least one activist.
He has warned alleged perpetrators of unrest that they would be "bashed" again if violence continued.
The European Union has ordered economic and political sanctions against Mugabe and senior officials believed to be responsible for the violent crackdown on the country's political opposition and banned more than 100 people from traveling to the 27-nation bloc.
It is not clear whether the new chairman would also face EU sanctions.