He was the most famous son (the fifth of ten children) of the anti-opium trade activist and General Secretary of the CIM Benjamin Broomhall and Amelia Hudson Taylor.
Marshall's father, Benjamin, then began 20 years of service as the China Inland Mission's general secretary at the London headquarters.
He attended a year at the CIM's Chinese Language School at Anqing, Anhui, and then he was appointed to the work in Taiyuan, Shanxi.
Florence Corderoy followed him to China in 1894, but mission regulations required that they could not marry until both had served for two years on the field.
Marshall had been transferred to Hongdong, Shanxi in 1896, to work with Dixon Edward Hoste, his brother-in-law, and with Gilbert Ritchie, who later married his sister, Edith.
As the tragedy unfolded and news was cabled to London, Marshall spent days and nights diligently sorting out information gathered from various sources and verifying rumours that were quickly circulating.
His hard work led to the compilation of two memorial books that documented the harrowing stories of both the martyrs and the survivors.
He wrote biographies of Hudson Taylor as well as several other members of the China Inland Mission, as well as several books that addressed overall issues and the history of the CIM.
In this commission constant reference was made to his important work The Chinese Empire: A General and Missionary Survey, and to the statistics in it.