In 2000, Stewart took leave from the Foreign Service to walk across Asia. This journey on foot lasted more than eighteen months and involved Stewart taking a 36-day solo walk across Afghanistan in the early months of 2002 and across much of Iran, Pakistan, and the Indian and Nepali Himalayas. He typically walked 20–25 miles a day, staying in village houses every night. He has also walked across sections of Western New Guinea and much of the United Kingdom. Stewart was awarded the Royal Scottish Geographical Society's Livingstone medal in 2009 "in recognition of his work in Afghanistan and his travel writing, and for his distinguished contribution to geography". His subsequent travel in the United Kingdom, and his writing on geography, was recognised by the Royal Geographical Society, which awarded him the Ness Award in 2018.