As a historian Marples has written extensively on Eastern European history of the 20th Century including such major historical events as the Russian Revolution 1917-1920, Ukrainian Famine 1932-1933, Stalinism, and fall of the Soviet Union. His most recent work concerns the NKVD executions in Belarus in 1937-1941 and mass burials at Kurapaty, Chajsy, and other sites.