J. Harleston Parker (1873 - May 5, 1930) was an American architect active in Boston, Massachusetts.
Parker was born in Boston, graduated from Harvard University in 1893, then studied architecture at the Massachusetts Institute of Technology and, after a further four years at the École des Beaux-Arts in Paris, took his degree in 1899. In 1900 he formed the firm of Parker & Thomas in Boston with Douglas H. Thomas, Jr., which later added Arthur W. Rice to become Parker, Thomas & Rice. As head of the firm, he designed many notable buildings and served as chairman of the Boston Art Commission. In 1921 he established the Harleston Parker Medal in memory of his father, awarded annually by the Boston Society of Architects and City of Boston to recognize “such architects as shall have, in the opinion of the Boston Society of Architects... completed the erection for any private citizen, association, corporation, or public authority, the most beautiful piece of architecture, building, monument or structure within the limits of the City of Boston or of the Metropolitan Parks District”.