He fought in the Second World War, played an influential role in the Malayan Emergency, then served as British Consul-General in Shanghai on the eve of the cultural revolution, as British Representative to North Vietnam during the Vietnam War, and as the Director of Technical Services and Assistant Chief of the Secret Intelligence Service (MI6) from 1974 to 1979.
During World War II, Stewart and his brother joined the Black Watch (Royal Highland Regiment), in which their grandfather had also served.
[5] He fought at the Battle of Rauray, to the west of Caen, as part of Operation Epsom, in which the unit he commanded claimed the destruction of 12 Panzer tanks, and where he was wounded.
[4] The key figure in his Malayan life, and great hero, was the High Commissioner, General Sir Gerald Templer, for whom Stewart pioneered the 'White Area' policy, whereby cooperative communities were relieved of the burdens of martial law.
[1] In 1974, he was invited back to become one of the three most senior figures in SIS, as Director of Technical Services, and he served as the de facto deputy of his friend and mentor Sir Maurice Oldfield.
[2] According to Oldfield's biographer, SIS colleagues had no doubt about Stewart's abilities as an intelligence officer but found his character "chilly – with a streak of arrogance.
Then, three years after leaving government, he became the Director of Operations in China for Racal Group, based in Hong Kong, leading their business in the newly opened Chinese economy.
Stewart is commemorated in a painting by Paul Benney, portraying him as a 92-year-old Normandy Veteran, commissioned by Charles, Prince of Wales, and held in the Royal Collection.