Subscribe to the BlogYvo de Boer, the UN's top climate change official, says he will resign after nearly four years in the post.
His departure takes effect from 1 July, five months before 193 countries are due to reconvene in Mexico for another attempt at a global deal on climate.
Nations failed to reach a binding deal at the Copenhagen meeting in December.
Mr de Boer said he was announcing his departure now so that a successor could be found well before the Mexico meeting later this year.
The former Dutch civil servant was appointed as executive secretary of the United Nations Framework Convention on Climate Change (UNFCCC) in 2006. As the UN's climate negotiator, he was widely credited with raising the profile of climate change issues.