As Washington's man at the United Nations, John Negroponte has frequently been at odds with the world body over Iraq and Israel amid concerns about US unilateralism.
At 64-years-old, the career diplomat is to head what will become America's largest embassy in the whole world, employing 3000 people.
He faces a growing resistance against the more than 130,000 US troops in the country, a creaking military coalition and ethnic and religious factions competing for the loudest political voice.
Viceroy or ambassador?
Clovis Maksoud, a former Arab League ambassador to the United Nations, said the appointment was a White House ploy.
He said the new ambassador's credentials were meant to leave the impression among Iraqis the power handover had some legitimacy because of the ambassador's UN connection.
"There is a projected symbolism that the UN is associated with the handover," Maksoud said, adding that the US military presence would help Negroponte act as much like a viceroy as an ambassador.
The British-born son of a Greek ship owner, Negroponte had sought to retire from tough assignments.
His career has seen him work in Vietnam, Honduras, Mexico and the Philippines.
He left government service in 1997 to join publisher McGraw-Hill as executive vice president for global markets.
[Negroponte's appointment] is a projected symbolism that the UN is associated with the handover"
former Arab league rep at UN
But Secretary of State Colin Powell, under whom Negroponte worked while Powell was national security adviser to President Ronald Reagan, persuaded him to quit that lucrative job and become ambassador to the United Nations in 2001.
"John Negroponte is a man of enormous experience and skill. That's why I'm comfortable in asking him to serve in this very difficult assignment," Bush told reporters in the Oval Office with Negroponte at his side on Monday.
At the United Nations, Negroponte stuck to US positions that were often unpopular with his Security Council colleagues.
He vetoed numerous compromise resolutions on the Israeli-Palestinian conflict and vowed to stop the UN's peacekeeping if the United States was not exempted from Prosecution by the International Criminal Court.
On Iraq, Negroponte helped craft Security Council resolution 1441 in 2002 giving Baghdad one last chance to hand over its elusive WMD.