The new government follows the "Revitalised agreement on the resolution of the conflict in the Republic of South Sudan" signed in September 2018 by South Sudan's warring parties The two main parties have agreed to join forces in running the conflict-affected nation and ending their years old differences. He called on their respective Dinka and Nuer ethnic groups to do the same.
A 2015 peace deal brought Machar back as vice-president and he returned to Juba with heavy security. Also present at the ceremony was the leader of Sudan, General Abdel Fattah al-Burhan.
Kiir and Machar have said outstanding issues will be negotiated under the new government.
The deal was supposed to have been finalised by May 2019 but was postponed twice - the latest deadline being 22 February.
South Sudan's President Salva Kiir, left, and opposition leader Riek Machar, who has been sworn in as his deputy. Pope Francis in a dramatic gesture kissed the feet of Kiir and Machar past year to coax them into putting differences aside.
Benjamin Okij, a refugee in Uganda, also told MEE that millions of Southern Sudanese were waiting for this moment as they had suffered from having no future, no hope and no jobs for a long time.
Margret Agostino, a Southern Sudanese student at Nairobi University, told MEE that the community of Southern Sudanese in Kenya were preparing to celebrate the peace deal.
The sticky issues were a formula to integrate tens of thousands of former rival forces into the country's united army and plans to reduce the number of administrative states in the country.
Crowds gather to greet Trump hours before he lands in India
But a senior White House official said that other deals in trade, energy and defence are likely to be announced during the visit. So obviously the post went viral, and Twitterati flooded the social media with their reactions.
And, with around 190,000 people still cowering in United Nations protection camps around the country, the UN special envoy to South Sudan David Shearer said he believed that "we will see lots of people once displaced moving back to their homes". Not all have signed on to the peace deal.
In a statement to the media by the presidency, Kiir reportedly reached a common ground with Dr. Machar and resolved to form the transitional government "on time".
It is hoped that the new unity government will bring an end to the conflict that has killed about 400,000 people and displaced millions. Another is Rebecca Garang, the widow of John Garang, who led a long fight for independence from Sudan. Some 40,000 are in starvation conditions, a new report said Thursday, and now a major locust outbreak in East Africa has arrived.
What is life like in South Sudan?.
Another more than 2 million people fled South Sudan during the civil war, and Kiir has urged them to come home.
The Sentry, an investigative team that has alleged corruption among some South Sudanese officials, urged the worldwide community to keep up pressure.
"But creating peace is more than just about forming a government".
"This is a typical vicious circle: poverty-conflict-peace lack of development then conflict", he says. Yet, in less than a decade, "we lost our way" and halted the momentum of a rising South Sudan that was at peace with itself and her neighbours.