Charles station was designed by H. Parker from the office of Richard Clipston Sturgis. The three-story headhouse structure, , was framed with steel and clad in cast stone. The first story had a rough finish, while the double-height second story and the third story (divided into two by the tracks) were smooth. The structure was Art Deco/Art Moderne in style, with decorative pilasters and a chevron panel. The platforms had copper windscreens, also in Art Deco style. A north-south pedestrian underpass crossed the traffic circle, with stairs leading from the underpass to the station entrance. Only the north half of the underpass was originally planned; public pressure resulted in the addition of the south half. A 14-story Art Deco tower over the station, designed by H. F. Kellogg, was proposed but never built.