Nathan Mossell was born in Hamilton, Canada in 1856, the fourth of six children. Both his parents, Eliza Bowers (1824 – ?) and Aaron Albert Mossell I (1824 – ?), were descended from freed slaves. During the Civil War, the family moved back to the United States, settling in Lockport, New York, where Mossell’s father again wned his own brickmaking business. He eventually joined his elder brother Charles at Lincoln University, a historically black college in Pennsylvania, where he studied Natural Science, receiving his Bachelor of Arts degree in 1879. Mossell went on to become the first African-American graduate of the University of Pennsylvania School of Medicine in 1882. He did post-graduate training at hospitals in Philadelphia, including the Pennsylvania University Hospital and later at Guy’s Hospital, Queen’s Hospital, and St Thomas’ Hospital in London. After his return to the United States, in 1888 he became the first black physician elected as member of the Philadelphia County Medical Society. That year he also started his private practice. In 1895, he helped found the Frederick Douglass Memorial Hospital and Training School in West Philadelphia, serving as its chief-of-staff and medical director until his retirement in 1933. After retiring as director of the hospital in 1933, Mossell continued to work in his private practice, which he had opened in 1888. He was believed to be the oldest practicing black physician at the age of his death.