Lewis was born in Chicago, Illinois, and raised in Detroit, Michigan. She attended the University of Michigan, where she studied theater. After graduating, she moved to New York City to pursue a career in acting.

Lewis's first major television role was as Regina Jones on A Different World. She also had a recurring role as Dr. Sydney Davenport on Chicago Hope. In 2004, she began starring as Captain Kathryn Hays on Battlestar Galactica.

Lewis is 5 feet 5 inches (1.65 meters) tall.