Andrew Natsios, a former director of the US Agency for International Development, flew into Khartoum on Friday.
The US administration had previously expressed concern about Khartoum's willingness to co-operate with its new envoy, but Sudanese officials insisted that Natsios had an important role.
"We welcome the visit of Mr Natsios to Sudan, and we will be listening to what he will say," Abdul-Basit al-Badawi al-Sanousi, the head of the US desk at Sudan's foreign ministry, said before he met Natsios.
Sudan has so far refused to accept UN forces in Darfur, the western region where an under-powered African Union force has been unable to curb escalating fighting between pro-government troops and militia and rebel groups.
More than 200,000 people have been killed and 2.5 million displaced since the violence began in Darfur in early 2003.
Natsios is hoping to visit Darfur and the newly autonomous south during his six-day visit, aides said in Washington before his departure.
State Department spokesman Sean McCormack said this week that the main purpose of Natsios' trip would be to encourage Sudan's government to clear the way for the deployment of 20,000 UN troops and police in Darfur.
The UN Security Council voted for such a force in August. At present there are 7,000 African Union peacekeepers in Darfur.
Meanwhile, Aljazeera has quoted Sam Ibok, the head of the African Union Team for the implementation of the Darfur peace agreement, as saying that efforts are continuing to make sure all groups join the Darfur-Darfur dialogue.
He said participants in the dialogue would be selected from the grass roots, explaining that selection would not be based on religious, ethnic or political criteria.
"The preparatory committee of the dialogue would comprise 25 members representing the Khartoum government, the African Union, the Arab League, the UN and the people of Darfur, including leaders of the civil society organisations and the native administration."