Born in Washington, D.C., Seymour received a Bachelor of Arts degree from Howard University in 1969 and a Juris Doctor from Washington College of Law at American University in 1977.
She was an equal opportunity specialist for the United States Department of Health, Education & Welfare from 1972 to 1979, and for the United States Equal Employment Opportunity Commission from 1979 to 1980.
She was an attorney in the Office of Civil Rights of the United States Department of Education from 1980 to 1988.
She was an Assistant United States Attorney of the District of South Carolina from 1990 to 1996, serving as the United States Attorney (interim) for that district from 1993 to 1996.
On September 9, 1998, Seymour was nominated by President Bill Clinton to a seat on the District of South Carolina vacated by William Byrd Traxler Jr.. She was confirmed by the United States Senate on October 21, 1998, and received her commission on October 22, 1998.