Al-Jaafari, whose tenure as prime minister of the interim government has been marred by continuing violence and little postwar rebuilding of the country's shattered infrastructure, edged out Iraqi Vice President Adil Abdul-Mahdi 63 votes to 62.
Mahdi's defeat came as a political shock, since he headed the largest group within the Shiite alliance, the Supreme Council for Islamic Revolution in Iraq, or SCIRI. But it was the 30 votes belonging to supporters of fiery Shiite cleric Muqtada al-Sadr that would decide the matter.
Al-Sadr is best known for his anti-American rhetoric that sparked a bloody wave of violence in 2004 and has expressed frustration with the continued presence of American forces in the region. The cleric's supporters told The New York Times that they had thrown their support to current prime minister because, "he promised to help carry out their political program," although there were few specifics on what al-Jaafari would do.
Despite the differences within the party, leaders publicly stressed that now that the United Iraqi Alliance had selected its premier, it would focus on building a governing coalition in parliament, where it will control 130 of the 275 seats in the new chamber.
"You should console me in this situation," The New York Times quoted al-Jaafari as telling Mahdi when the latter congratulated him. "This is a big burden and a position of difficulties."
But beyond the difficulty awaiting al-Jaafari, he added he would build a government aimed at benefiting all Iraqis.
"[Sunday]'s victory is not that this one won or that one won," al-Jaafari said. "It is a victory of the (Shiite) alliance with its unity and cool head."
In addition to signaling his desire for a unified Shiite party, al-Jaafari said he would take a tough stance with the minority Sunni population, demanding Sunnis support the new constitution and join the fight against insurgents.
"The main basis for dialogue will primarily be the constitution, respect for the constitution and its contents after the people ratified and adopted it," al-Jaafari said.
Sunni politicians offered al-Jaafari a lukewarm response, using his selection as an opportunity to question the performance of the government the Shiite has headed.
"We have some reservations, not on the person of Dr. al-Jaafari, but on the performance of his government," Naseer al-Ani, a Sunni Arab politician, told the Associated Press. "We believe that his government's performance on security and services was irresponsible."
On the streets of Iraq, citizens offered mixed reviews of the selection, saying that al-Jaafari was well suited to form a consensus, but expressing skepticism of the job he has done as interim prime minister.
"I expect a tragic end for Iraq with Jaafari keeping his position," Falih Abdul Qadir Latif, owner of an electrical store in Baquba, told Reuters. This man is not able to present any solutions; the problems Iraqis and Iraq are facing are evidence of his failure. We have to face the next four years reluctantly."