The 37-year-old Grammy-winning country star is "thrilled beyond belief," says Sugarland manager Gail Gellman.
The baby is due around the couple's first wedding anniversary. Nettles and Miller wed last November in the Smokey Mountains.
Nettles and Kristian Bush make up the platinum-selling country duo Sugarland. They have such hits as "All I Want To Do," "Stay," and "Stuck Like Glue."
The Associated Press contributed to this report.
