St. Mary's Episcopal Church is the most significant Boston commission of English architect Henry Vaughan, who later designed the
National Cathedral
in Washington, D.C., with George Frederick Bodley. Vaughan based the design on fifteenth-century English parish church precedents. The church is ornamented by elaborate half timbering on the exterior, a complex timber-frame ceiling, and an especially fine collection of stained glass, including the work of Tiffany Studios, A. B. Cutter Company, and the Charles Connick Studio. In 1893, Hartwell and Richardson added the transepts and chancel; Charles K. Cummings designed the adjacent parish house in 1907.