Reuben David Sassoon was born in 1835. His father was David Sassoon (1792–1864), a Jewish trader of opium and cotton in China who served as the Treasurer of Baghdad from 1817 to 1829. One of his brothers was Arthur Sassoon (1840–1912). He worked for his father's company, serving as director of David Sassoon & Co. for East India and China. By 1865, he also served on the board of directors of the China Steamship and Labuan Coal Company alongside T.C. Bruce, Sir J.D. Elphinstone, Harry Borradaile, H.B. Loch, Henry Alers Hankey, William Miller, Edward Pereira, G. Lathom Brown, Alexander Sinclair, James N. Daniel and John Hickie.