Stewart-Lockhart came from a noble, wealthy family. His father, Miles Lockhart, was a banker.
He was taught by a private tutor, then went to King William's College, later George Watson School and Edinburgh University, where he got a prize for Greek Studies.
He came to Hong Kong as a cadet in 1879. He took up a post of the registrar general in 1883.
He became the colonial secretary in 1895. One of his remarkable jobs was the takeover of the New Territories. He wrote a report to the Government about the society of the New Territories and the suggestions of ruling the newly leased land. He also accompanied the troops during the six-day war.
He was transferred to Weihaiwei as a commissioner in 1902. Nevertheless, he was connected to the Chinese Notables. For example, he invited the leaders to donate for the flooding in Northern China.
He retired in 1921 and took up the post at London University. He died in 1937.
He was keen on Chinese Culture. he wrote a book, "Chinese Quotations" in 1894. He also published books about Chinese Coins and the history of Taiping Heavenly Kingdom.