The Parliament largely avoided responding because reforms and new elections would likely mean that many established political groups would lose power. The country’s senior religious authorities have largely sided with the protesters in demanding change and their pressure led the prime minister to resign at the end of November.

Since then, neither the Parliament nor the president has been able to find a prime minister candidate on which both the Parliament and the protesters could agree.

The selection of Mr. Allawi is an effort to pick someone who has worked with a wide range of political parties and who is educated and secular as well as having the requisite Shiite Muslim background.

Since the toppling of Saddam Hussein, Iraq has had a political power sharing agreement whereby the prime minister comes from the country’s Shiite Muslim majority, the speaker of the parliament is from the Sunni Muslim minority and the president is of Kurdish ethnicity so that all three main ethnic and religious groups are represented.

Mr. Allawi was educated initially in Baghdad but then went to Beirut to completely his studies in architecture. He lived for years in London and was active in the Iraqi opposition. As a young man, he was drawn to the Dawa party many of whose members have close ties to Iran.

But after the toppling of Saddam Hussein, he began to align himself with his cousin, Iyad Allawi, who was the interim prime minister in 2004, and eventually joined Iraqiya, his cousin’s political party. It is a secular party that includes Sunni and Shiite Muslims as well as Christians and a number of women, but it has few seats in the Parliament compared to the religious parties.

Within minutes of his nomination, he got an endorsement from the powerful Shiite cleric and political leader Moktada al-Sadr, who controls the largest bloc in Parliament.