Barbara Neely, an unheralded social activist who in her 50s became an award-winning writer of mystery novels centered on a savvy black maid who doubles as an amateur detective, died on March 2 in Philadelphia. She was 78.

Ms. Neely’s family announced her death through her publisher, Brash Books, without providing further details, except to say that she had been ill for a short time.

Ms. Neely was not the first black female mystery writer. Nor was Blanche White the first fictional black sleuth. But Blanche was probably the first fictional black maid to solve a murder while working for a wealthy white family, and to go on to become an avocational gumshoe in a series of books from a mainstream American publisher.

Blanche was an opinionated woman, imbued with the passion of the author. Ms. Neely had taught prison inmates, fought for abortion rights, assailed violence against women and, through her activism and storytelling, ennobled working mothers, defied stereotypes and confronted bigotry and class discrimination, both directed against blacks and within the black community.