After the war, Singh served as regent of Rewa State from October 1918 to October 1922. He also served in the Third Anglo-Afghan War as aide-de-camp to the General Officer Commanding 1st Division on the North-West Frontier. From 1915 to 1936, Sajjan Singh served as aide-de-camp to George V and was also aide-de-camp to the Prince of Wales (later Edward VIII) when the latter toured India from 1921 to 1922; he was appointed a KCVO for this in 1922. Singh subsequently served as an honorary and extra ADC to George VI until 1947.