While in Kingston he served as secretary and president of the Kingston Historical Society and edited "Historic Kingston" for several years. He was president of the Arts Society, director of the Art Collection Society, served on various committees working to save Kingston's old limestone buildings, was president of the St. Andrew's Society, and acted as clerk of his church's vestry council. Stanley was president of the Canadian Historical Association (1955–1956), a member of the Massey Commission's Committee on Historic Sites and Monuments (1950–1951), and a founding member of the Archaeological and Historic Sites Board of Ontario (1953–1969). He was chairman of the federal government's Centennial Publications Committee and acted as chairman of centennial celebrations in Pittsburgh Township, Ontario. While Stanley was at the Royal Military College, he suggested the design for the Canadian flag, which was adopted on 15 February 1965.