Iraqi Shia leader Ibrahim Jaafari has been named prime minister of the country's new interim government.
Mr Jaafari heads the Daawa party, part of Iraq's Shia alliance
He was appointed shortly after Kurdish leader Jalal Talabani was sworn in as Iraq's new interim president.
Outgoing Prime Minister Iyad Allawi has resigned, but will continue his work until Mr Jaafari names his government.
The transitional government's main task will be to oversee the drafting of a permanent Iraqi constitution and to pave the way for elections in December.
Mr Jaafari, 58, is seen as one of Iraq's most popular political figures.
He has up to a month to name his team, but indicated that he hoped to announce a new government within two weeks.
"Today represents a big step forward for Iraq and a big responsibility for me," he said.
Born Karbala, 1947
Educated at Mosul university as a medical doctor
Lived in Iran and UK since 1980s
Spokesman for the Islamic Daawa party
Preferred candidate of Shia United Iraqi Alliance
Served as vice-president in US-appointed regime
The presidential swearing-in ceremony took place before the parliament in the heavily-fortified Green Zone in central Baghdad.
Mr Talabani's deputies, Adel Abdul-Mahdi, a Shia, and the outgoing President, Ghazi Yawer, a Sunni, have also taken the oath of office.
"We will rebuild the Iraqi government on principles of democracy, human rights... and the Islamic identity of the Iraqi government," Mr Talabani told a special session of parliament.
"[It will] preserve the liberty for all, where all the citizens, whether Shia or Sunni, will be brothers.
The BBC's Caroline Hawley in Baghdad says this is a highly symbolic moment for both the Shia and the Kurds.
After being brutally repressed under Saddam Hussein, they are now taking the reins of power in Iraq.
Ousted Iraqi leader Saddam Hussein watched the session on television in jail, officials said.
Members of the new parliament, dressed in tribal robes, business suits and religious garments, cast their secret ballots for the three-man presidency council in the assembly inside Baghdad's fortified Green Zone.
The votes were then counted publicly.
The appointment of Mr Talabani, leader of the Patriotic Union of Kurdistan, makes room for Kurdistan Democratic Party chief Massoud Barzani - his long-time rival - to head an autonomous government in the Kurdish region in the north of Iraq.
Some critics of the system have labelled the new political structure a "sectarian carve-up" of Iraq.
"The old wounds I think are getting deeper," Sheikh Fawaz al-Jarba, second cousin of new Sunni Vice-President Ghazi Yawer, told the AFP news agency.
"This is a farce. Everything is pre-ordained and pre-arranged before lawmakers convene."