The establishment of the new parliament constitutes a milestone in the implementation of the Comprehensive Peace Agreement (CPA), signed on 9 January by the Sudanese government and the former southern rebels of the Sudan People's Liberation Movement/Army (SPLM/A).
It also represents an important step in fulfilling the southerners' aspirations for greater political autonomy and the decentralisation of power, for which the SPLM/A fought during a 21-year war that claimed two million lives.
"This is clearly a significant and historic moment. This is what people have been waiting for since the signing of the CPA, and probably for the past 20 years," David Gressly, the UN deputy resident and humanitarian coordinator for southern Sudan, told IRIN at the ceremony.
"With the establishment of the new assembly, the south will have the ability to govern its own affairs," he added.
One of the first tasks of the new parliament would be to ratify the new southern Sudanese constitution, which would pave the way for the formation of a new southern government and the establishment of the various ministries.
"It is symbolically significant that all the groups that were formerly divided - the different militias, the political representatives - are together here today," a political analyst, who requested anonymity, said. "You can't heal wounds unless you're actually coming together."
He added: "The signing of the peace agreement was one thing - but not everybody believed it. The new parliament is now a concrete fact and every step further cements people's belief in a better future."
The establishment of the legislative council also opens the door for the adoption of a host of new legislative powers - from approving budgets to decisions on the framework of local governance - that are essential for the implementation of development and reconstruction programmes for the war-ravaged region.
"We stand ready to support the new government institutions as they are formed and look forward to working with the new government as they take a leadership role in the development of southern Sudan," Gressly said.
During the ceremony - attended by the Sudanese first vice-president and president of southern Sudan, Salva Kiir Mayardit, and southern Sudanese Vice-President, Riek Machar - James Wani Igga was elected Speaker of the new legislative and Tor Deng became Deputy Speaker.
Igga, a former secretary-general of the SPLM/A, is considered the third-highest ranking member of the movement. Tor Deng, a former minister of education, is a member of the ruling National Congress Party in the Sudanese capital, Khartoum.
"This [the election of Deng] is once more a confirmation of our commitment to the cooperation with the National Congress Party," Igga told the new legislative.
The transitional southern parliament will remain in place until legislative elections are held in approximately four years. After a six-year interim period, which began on 9 July, the south will hold a referendum to decide whether to remain part of a united Sudan or secede.
During the ceremony, Kiir said the major tasks of the government of southern Sudan included the provision of health, education, water and food services.
The official Sudanese news agency, SUNA, reported that Kiir also announced that an institution would be set up to combat corruption in the south and called on the new assembly to adhere to its supervisory role.