Guterres is appointing veteran Norwegian diplomat Geir O. Pedersen to assume the post de Mistura will depart in late November after serving more than four years as the UN's point person for the conflict in Syria.
Pedersen will be the fourth person to hold the position after former UN Secretary General Kofi Annon and Algerian envoy Lakhdar Brahimi quit the post in 2012 and 2014, respectively.
De Mistura has been running intra-Syrian talks since late 2017 seeking to draft a new constitution for Syria and establish requirements for UN-supervised elections.
"The Secretary-General takes this opportunity to reiterate his deepest gratitude to Staffan de Mistura of Italy for his concerted efforts and contributions to the search for peace in Syria," the UN said in a statement.
The leaders of Turkey, Russia, Germany and France met last weekend to discuss the situation in Syria, ultimately calling for a new constitution and free and fair elections in the war-torn country.
Source: Anadolu Agency