Duncan then served for one year as a law clerk to Judge Julia Cooper Mack of the District of Columbia Court of Appeals from 1977 to 1978.

[2] Duncan was appointed a Commissioner of the North Carolina Utilities Commission in 1991 and remained in that post until 1998, when she joined the Raleigh office of Kilpatrick Stockton as a partner.

[3] Duncan was nominated on April 28, 2003, by President George W. Bush to fill a vacancy on the Fourth Circuit created by Judge Samuel James Ervin III, who died on September 18, 1999.

A Republican, Duncan was supported by both Senators Elizabeth Dole and John Edwards, a departure from the trend toward partisan controversy over North Carolina appointments to the Fourth Circuit Court of Appeals.

[7] In September 2018, President Donald Trump nominated Allison Jones Rushing to replace Duncan on the 4th Circuit Court.