Benjamin Louis Simpson was born on July 15, 1818, in Baltimore, Maryland. He married Sarah P. Waters, and they had at least four children: Richard, born around 1845; Benjamin, born around 1847; Ida, born around 1850; and Maria, born around 1860. They lived in Baltimore, Maryland, and he worked as a ship carpenter. By 1850, he owned $2,000 of real estate.
He remained loyal to the Union during the Civil War. In 1861, he received a commission as captain of Company A of Purnell’s Legion, Maryland Infantry. The following year, he was promoted to major and then to lieutenant colonel. The regiment took part in the Battle of Antietam. He resigned on January 14, 1863.
He rejoined the Union army in the summer of 1863, mustering in as lieutenant colonel of the 9th Maryland Infantry. He later received a promotion to colonel, and he mustered out on February 24, 1864.
He moved to Washington, D.C., after the war, and he served as foreman of the Washington Navy Yard. He died of phthisis pulmonalis tuberculosis in Washington on February 27, 1888.