Field Marshal Sir Donald Martin Stewart, 1st Baronet, was a senior Indian Army officer. He fought on the Aka Khel Expedition to the North-West Frontier in 1854, took part in the response to the Indian Rebellion in 1857 and, after serving as commandant of the penal settlement of the Andaman Islands, fought in the Second Anglo-Afghan War as Commander of the Quetta Army. In that role, he advanced through the Bolan Pass to Quetta, and then on to Kandahar in January 1879. In March 1880, he made a difficult march from Kandahar to Kabul, fighting on the way the Battle of Ahmed Khel and Battle of Arzu, and then holding supreme military and civil command in northern Afghanistan. He became Commander-in-Chief, India in April 1881 and a member of the Council of the Secretary of State for India in 1893.

Field marshal (FM) has been the highest rank in the British Army since 1736. A five-star rank with NATO code OF-10, it is equivalent to an Admiral of the Fleet in the Royal Navy or a Marshal of the Royal Air Force in the Royal Air Force (RAF). A Field Marshal's insignia consists of two crossed batons surrounded by yellow leaves below the Tudor Crown. Like Marshals of the Royal Air Force and Admirals of the Fleet, Field Marshals traditionally remain officers for life, though on half-pay when not in an appointment or retired. The rank has been used sporadically throughout its history, and was vacant during parts of the 18th and 19th centuries. After the Second World War, it became standard practice to appoint the Chief of the Imperial General Staff to the rank on his last day in the post. Army officers occupying the post of Chief of the Defence Staff, the professional head of all the British Armed Forces, were usually promoted to the rank upon their appointment.