Marshall returned to school to study law at the Norman Adrian Wiggins School of Law at Campbell University and earned her Juris Doctor (J.D.) degree in 1981, where she was accepted into the Who's Who Among American Universities and Colleges. She has been admitted to practice before all North Carolina courts, the U.S. District courts in the Eastern and Middle Districts of North Carolina, the U.S. Fourth Circuit Court of Appeals, and the United States Supreme Court. She is a member of the NC State Bar, the NC Bar Association, the NC Association of Women Attorneys, and the Delta Theta Phi legal fraternity. She became a partner in a Lillington, North Carolina, law firm in 1985.