Born in British Hong Kong, Stewart was educated at the Dragon School and Eton College. After studying at Balliol College, Oxford, Stewart worked for the Foreign Office serving as a diplomat in Indonesia and as British Representative to Montenegro. He left diplomatic service to undertake a two-year walk across Afghanistan, Iran, Pakistan, India and Nepal. He later wrote a best-selling book, "The Places in Between", about his experiences. He subsequently served as a Deputy Governor for the Coalition Provisional Authority following the 2003 invasion of Iraq, and wrote a second book covering this period, "". In 2005, he moved to Kabul to establish and run the Turquoise Mountain Foundation. He was the Ryan Family Professor of Human Rights and the Director of the Carr Center for Human Rights Policy at Harvard University from 2008 to 2010.