"By taking this crucial step, the Council of Representatives has demonstrated its commitment to unite the country," Xinhua quoted US State Department spokeswoman Marie Harf as saying.
Mohammed Fuad Masoum Thursday was elected as the new president of Iraq.
Masoum, 76, was the first prime minister of the semi-autonomous Iraqi Kurdistan in 1992.
He is a leading figure in the Patriotic Union of Kurdistan, headed by outgoing President Jalal Talabani.
Masoum also headed the Kurdistan Alliance in the Iraqi parliament since 2005.
The Kurds nominated Masoum a few days after the ailing Talabani, 81, returned from 18 months of medical treatment in Germany.
Masoum won 211 votes from 269 lawmakers who attended the session of the 328-seat parliament.
The US has also urged Iraqi leaders to form an inclusive government to address the threat of the Islamist militants.
"Only with an inclusive, cohesive government that represents all Iraqis, can the country most effectively and successfully confront the urgent security and humanitarian challenges it faces in the fight against Islamic militants," Harf said.
Iraq's leaders must take the next step in their democratic process by choosing a prime minister and forming a government, Harf added.