Prior to her mother's death, she was adopted by the family of the American Civil War veteran and social activist Lloyd G. Seymour.

In June 1888, at the age of fifteen, she visited the City Hall to review her birth certificates and declared her official name as Mary Emma Townsend Seymour.

On October 9, 1917, the Hartford chapter of the National Association for the Advancement of Colored People (NAACP) was founded, with Seymour serving as its spokesperson.

[4] As part of her activities with the NAACP, she went undercover to investigate the treatment of women tobacco workers, and worked to publicize their plight.

She and fellow activist Josephine Bennett interviewed female laborers, and co-wrote an exposé on the subject for The Crisis in 1920.