The doctor, who has not been identified, wore a full-body biohazard suit as he walked gingerly into the hospital where two other Americans were successfully treated, television images showed.
The patient is a US citizen who was working in Sierra Leone when he tested positive for the lethal virus, according to the State Department, which helped evacuate the doctor on a private chartered flight.
"Every precaution was taken to move the patient safely and securely, to provide critical care en route, and to maintain strict isolation upon arrival in the United States," department spokeswoman Marie Harf said in a statement.
The World Health Organization said on Monday that one of its doctors was being evacuated from Freetown after contracting the virus but would not disclose where the health care worker was going. A US health official, who requested anonymity, said that doctor was the one who arrived in Atlanta.
Emory confirmed on Tuesday that a third Ebola patient had been admitted to its facility after being flown from West Africa.
A fourth American, missionary Dr. Rick Sacra, was being treated in Omaha after becoming infected with Ebola in Liberia.
Doctors at the Nebraska Medical Center said on Tuesday that Sacra's condition continued to improve in an isolation unit. He has been speaking regularly with family through a video link.
"We're pleased with his progress," Dr. Phil Smith said in a statement. "His lab values are improving and he's becoming more alert and interactive. We continue to be encouraged by what we're seeing up to this point."
The new Atlanta patient will be treated in the same isolation unit for serious infectious diseases where US missionaries Nancy Writebol and Dr. Kent Brantly were treated before being discharged last month, Emory said.
Medical workers have been hit hard by the epidemic, the worst since Ebola was discovered in 1976. As of late August, more than 240 health care workers had developed the disease and more than 120 had died, according to WHO.The outbreak has killed at least 2,296 people out of 4,293 cases in five West African countries, WHO said on Tuesday.