As a journalist, Gertrude wrote for a myriad of publications; she became the woman’s editor of the New York Freeman, the Indianapolis World, and the New York Age, which was the most widely read newspaper in black America at the time. She also wrote syndicated columns for the Press Republican, the Philadelphia Times, the Philadelphia Echo, and the Philadelphia Independent. Gertrude also contributed individual articles to the Franklin Rankin Institute, Our Women and Children, and the AME Church Review.  As a black “feminist,” Gertrude wrote columns encouraging black women to submit articles to publications, pushing for more female inclusion in the field of journalism as early as 1886; and as a political activist, Gertrude openly wrote about political and social issues.

Gertrude was very progressive for her time as an outspoken and active member of the women's suffrage movement, and a proponent of women’s rights. Upholding a "renaissance woman" philosophy, Gertrude encouraged black women to enter the careers of medicine, business, and journalism, while simultaneously managing their household affairs and family duties as mothers.  In 1894, Gertrude wrote and published a powerful book entitled, The Work of the Afro-American Woman which is a collection of essays and poems that chronicled the work and accomplishments of thousands of black women in various fields, including medicine, law, education, journalism, literature, business, and music. This was a pivotal work because it highlighted the achievements of many black women who were unknown at the time, and proved to the world that African American women were not simply sterotypical domestic servants, but highly active and intelligent.

Gertrude was also heavily involved with community improvement and social welfare.  She founded the Bustill Family Association, headed the committees of the Social Service Auxiliary and the National Afro-American Council (the first truly nationwide civil rights organization in the United States that pre-dated the NAACP), and Gertrude was instrumental in raising money to build the Frederick Douglass Memorial Hospital and Training School that served black patients, who were often turned away by white hospitals.

On July 12, 1880 Gertrude Emily Hicks Bustill married Nathaniel F. Mossell, a prominent Philadelphia physician, and the first African American to earn a medical degree from the University of Pennsylvania.  Gertrude and Nathan had 2 children survive to adulthood, Mary and Florence Mossell.  Admirably, Gertrude Bustill Mossell accomplished all that she did while raising a family, and still maintained the role of devoted wife and mother.