Speaking at a peace ceremony in Juba on Wednesday, the rebel chief said he was ready to give peace a chance in the war-torn country.
He announced that the new peace deal will lead to the creation of a federal government.
Machar returned to Juba for the first time in more than two years to take part in a peace ceremony.
South Sudan main opposition leader Riek Machar has reiterated his commitment to the implementation of the peace deal.
Speaking at a peace ceremony in Juba on Wednesday, the rebel chief said he was ready to give peace a chance in the war-torn country.
"We come here today [Wednesday] to confirm to you that we are for peace...We want peace and unity," Machar told the crowd at Freedom Square.
Machar called on President Salva Kiir for the release of political detainees in the country.
"We aware after the crisis in 2016, some people were arrested. So, political prisoners should be released all," said Machar.
He announced that the new peace deal will lead to the creation of a federal government.
"The peace agreement will bring you federal system of governance," he said.
Machar returned to Juba for the first time in more than two years to take part in the ceremony.
Somali President Mohamed Abdullahi Farmajo, who attended the ceremony, urged all the parties to the conflict to commit themselves to the implementation of the September peace agreement in letter and spirit.
A Mo Ibrahim Foundation report recently ranked South Sudan as the second worst governed state in Africa after Somalia.
South Sudan plunged into a civil war in 2013 when President Kiir accused Machar —then vice president— of plotting a coup against him.
Several peace accords have been signed but faltered immediately including the last one in 2016 that forced Machar to flee into exile.