He served as Ceylon's Trade Commissioner and a District Judge[1] and held multiple appointments as president of the Royal Asiatic Society of Sri Lanka.
Although his academic and early career was in the legal field, he is best known for being one of the country's foremost experts on the history of European occupation of Sri Lanka.
[citation needed] Pieris won the University scholarship in 1891 and became the first Asian to be admitted to Trinity College, Cambridge where he gained BA (which was later upgraded to a MA), LLM and Litt.D.(Cantab).
[1][4][2] It has been remarked that Pieris was never given a position in the Civil Service that was commensurate with his intellect and ability, and as such he turned his attention toward in depth historical research on the European occupation in Ceylon from the 16th Century onwards.
He further single-handedly edited the journal during the years of World War II when the society's functions were greatly disrupted by external factors.