The head of Igad's Joint Monitoring and Evaluation Commission (JMEC) for South Sudan, Mr Festus Mogae, has announced his resignation.
Mr Mogae said Monday that he has submitted his resignation letter to the Intergovernmental Authority on Development chairman Ethiopian Prime Minister Ahmed Abiy.
The former Botswana president in his quit notice said he will be stepping down to allow new leadership during South Sudan's transition phase.
"As the process of revitalise the agreement on the resolution of the conflict in the Republic of South Sudan draws to a close, I have adjudged it appropriate to allow for the new phase of the transitional period for South Sudan to be in fresh hands," he said in a statement.
He is expected to end his service at the end of September.
His resignation comes as South Sudan warring parties sealed a new peace agreement in Khartoum in talks that ended on Sunday.
The agreement compels President Salva Kiir and his former deputy Riek Machar to work together again.
JMEC was established under the terms of the August 2015 South Sudan peace agreement to monitor, and oversee the implementation of the deal.
The pact however broke down after fresh fighting erupted a year later.
In the latest deal, has however made major strides compared with previous efforts to stop the five-year civil war.
In the next eight months, during the pre-trial period, the warring parties must form a Cabinet of 35 members, appoint new members of parliament, constitute the National Boundary Committee and integrate the armed groups into a single national army.
Festus Gontebanye Mogae, was born on August 21, 1939 in Serowe in the Central district of Botswana.
- Education: Studied economics at the universities of Oxford and Sussex in the United Kingdom, graduating in 1974.
1975 – 1976: Permanent secretary to the president
1976 to 1980: Executive director, IMF for Anglophone Africa.
1980 to 1981: Governor of the Bank of Botswana.
1982 -1989: Permanent secretary to the president.
1989: Minister of finance and development planning.
1992 – 1999: Vice president of Botswana.
October 1999: President of Botswana.
April 2008: Stepped down as president 18 months before the end of his term.
2008: Became the second winner of the Ibrahim Prize for Achievement in African Leadership.