The UN’s top climate diplomat, Christiana Figueres, has said she will leave her post in July.
Ms Figueres said she would not accept an extension of her appointment which finishes this summer.
As executive secretary of the UN Framework Convention on Climate Change, she played a key role in the talks that lead to the Paris Climate Agreement.
Her contribution to the negotiation process was praised as “really extraordinary”.
Ms Figueres became executive secretary in the wake of the Copenhagen climate conference in 2009, widely perceived to have been a failure.
Over the past six years she helped rebuilt the momentum for a global compact, which saw 195 nations sign the Paris Climate Agreement after weeks of intense negotiations in the French capital last December.
In her letter to the UN confirming that she was standing down, the 59-year-old Ms Figueres highlighted the importance of that deal.
“The Paris Agreement is a historical achievement, built on years of increasing willingness to construct bridges of collaboration and solidarity. It has been an honour to support you along this path over the past six years,” she wrote.
Before taking the UN post in 2010, Ms Figueres had been part of Costa Rica’s climate negotiating team since the mid 1990s.