The inauguration is set for Saturday in the capital, Khartoum.
John Garang, chairman of the SPLM/A, was expected to arrive in Khartoum on Friday for the first time in more than 22 years. He will be sworn in as First Vice President of the new government and President of a semi-autonomous southern region. Incumbent Umar Al-Bashir will remain president.
Following the parliamentary ratification, Ali Uthman Muhammad Taha, who is to become Second Vice President, told the members of the national assembly to "practice sound and responsible politics through dialogue", and honour the values which were contained in the constitution.
The SPLM/A's legislative council, which unanimously passed the transitional constitution after a three- day debate, called it "historical...a genuine beginning of the implementation of the peace accord".
On 9 January, the Sudanese government and the SPLM/A signed a Comprehensive Peace Agreement (CPA), ending more than 20 years of civil war that left an estimated two million people dead and four million displaced.
The CPA provided for a government of national unity - based on a transitional constitution - and a six-year interim period. Following this interim period, a referendum would decide whether the south would remain part of the country or become independent.
Amnesty International (AI), however, expressed concerns in a statement on Wednesday regarding the high level of immunity the new constitution granted to senior government officials.
"Although we welcome some of the human rights provisions in the new constitution, particularly the greater emphasis placed on the rights of women and children, we have serious concerns that [it] grants high level immunity from prosecution for most crimes," Kolawole Olaniyan, director of AI’s Africa programme, said.
"It is extremely troubling that in the context of one of the most serious conflicts in the world, in which tens of thousands of Sudanese have been the victims of gross human rights violations, a new interim constitution would be approved that neglects to cite international crimes such as war crimes and crimes against humanity as crimes that should never carry immunity - no matter what level of government the alleged perpetrator might occupy," Olaniyan added.
The interim constitution grants immunity from prosecution for most crimes, for the President and First Vice President, as well as for members of the national legislature.
AI also feared that last-minute constitutional amendments left the door open for punishments such as flogging and amputation, which remain legal under Sudanese law.
It expressed serious concerns regarding the upholding of the death penalty in Sudan - particularly with regard to people under the age of 18.
UN Secretary-General Kofi Annan is among those expected in Khartoum to attend the ceremony, along with a number of heads of state, a spokesman for the Secretary-General, Stephane Dujarric, told reporters on Wednesday.
"The Secretary-General’s visit comes at a time of a funding shortfall for humanitarian programmes in the Sudan," he said.
"As of the end of June, of the required US $1.3 billion, only $643 million has been received. This means that critically important programmes cannot be carried out in full or, in some cases, at all," he added.
The ceremony will coincide with the lifting of the country’s 16-year-old state of emergency and the start of the interim period.
According to the CPA, the ruling National Congress Party (NCP) will have 52 percent of executive posts and legislative seats and the SPLM/A 28 percent during the first four years.
Fourteen out of the remaining 20 percent will go to northern opposition parties, with six percent to be split among other southern groups.
In the south, a regional government, parliament and judiciary will be set up with 70 percent allotted to the SPLM/A, 15 percent to the NCP and the remaining 15 percent to other political forces.
Key strategic interests such as national defence, foreign policy, national economic policy and planning will remain the responsibility of the national government, while a joint oil commission will be the sole authority to award concessions.
At the start of the interim period, the SPLM/A has between six and 15 months left to withdraw its forces from its positions in northern Sudan. The national army has another 24 months to pull out of southern Sudan.
Both forces should have started their withdrawal immediately after the January peace deal, but have fallen behind schedule. Sources said there were concerns that several southern militia commanders had not yet signed on to the CPA. It was also unclear how or whether they would be represented in the interim institutions.
The UN Mission in Sudan, which started the deployment of a 10,000-strong peacekeeping force in April, is mandated to assist both parties in disarming fighters and removing landmines, and will also support development projects and the repatriation of people displaced by the conflict.