Stewart was born in Strichen, Aberdeenshire, Scotland, and educated at the University of Aberdeen where he graduated with first-class honours in classics in 1903. He passed the Indian civil service examination in 1904 and went to Myanmar in 1905. He worked for five years in the Settlement (Land Revenue) Department where he met J S Furnivall. During the First World War, and the Anglo-Afghan War, Stewart served for 4 and a half years with the Burma Sappers and Miners in Mesopotamia (where he was awarded the Military Cross) and Persia. He returned to Myanmar and was Commissioner of the Magwe Division in the 1930s. With C W. Dunn he compiled the first Burmese-English dictionary, published under the auspices of the University of Rangoon, in five volumes, the first volume published in 1940, but the project remained incomplete at the time of his death.