Former President Mary Robinson has been appointed as United Nations Special Envoy for Climate Change.
The appointment comes ahead of a climate summit involving international leaders in September, which will be hosted by the UN.
UN Secretary-General Ban Ki-moon asked Ms Robinson to relinquish her role as Special Envoy for the Great Lakes region of Africa to take up the new position.
Ms Robinson will stay in the role until climate talks in Paris in December 2015.
She said: "I have mixed emotions at handing over the role in the Great Lakes region when I make my final report to the Security Council on 7 August, but ultimately I feel it is appropriate that I respond positively to the request of the Secretary-General.
"His focus on climate change and his faith in my capacity to help make progress on the challenges it presents is, I believe, an affirmation of the work of the foundation I lead.
"Our work on climate justice emphasises the urgency of action on climate change from a people's perspective and I intend to take this approach in my new mandate as Special Envoy for Climate Change."
Ms Robinson, who served as President from 1990 to 1997, was previously UN High Commissioner for Human Rights from 1997 to 2002.