St. Paul's is one of the country's foremost examples of the Greek Revival style, an architectural mode popular in America and Europe in the second quarter of the 19th century. Architect Thomas S. Stewart of Philadelphia was commissioned to design the church based on his design for St. Luke's Church (now The Church of St. Luke and the Epiphany) in Philadelphia Built of brick rendered with stucco, the main body of the building is in the form of a classical temple. The portico columns are in the Greek Corinthian order of the Choragic Monument of Lysicrates, an ancient monument in Athens. The wooden column shafts are topped with richly articulated capitals of cast iron. A striking but now lost original feature was an octagonal spire atop the steeple belfry, reaching to an overall height of 115 feet from street level. The spire was removed following a hurricane in 1900, and replaced by a small dome over the belfry. The capitals of the belfry piers employ a modified version of the Corinthian order from the Tower of the Winds, another ancient Athenian monument. Housed in the belfry is a peal of bells that plays the Westminster chimes on the quarter-hour. The circular panels immediately below the belfry were meant for clock faces.
St. Paul's was built during a period when the Episcopal Church was dominated by "Low Church" or Protestant tradition, which meant that it eschewed the heavy iconography of the Roman Catholic Church. As a result, no Christian religious symbols were originally incorporated into its design. All of its architectural decoration was based on ancient Greek forms and details. This is vividly apparent in the interior, where the nave is dominated by a magnificent plaster-work ceiling encrusted with Greek-style decorations. One exception to this avoidance of religious symbols is the ceiling's focal point: in its center is a gilded triangle - a symbol of the Trinity - enclosing the Hebrew Tetragrammaton, the four Hebrew letters spelling the name Yahweh (God). The triangle is surrounded by gilded rays that were part of the building's original ventilation system.
Other Greek-style architectural decorations include the chancel columns, which employ the same Greek Corinthian order as the front portico. The ends of the original pews are finely carved with Grecian tendrils. The frontal panels of the gallery are decorated with several types of Greek floral designs. The pilaster capitals on the walls around the interior are based on a Greek-style adaptation by the New York architect Minard Lafever and published in his pattern book, The Beauties of Modern Architecture (1835).
St. Paul's was the largest Episcopal Church in Virginia at the time of its completion, and could seat a thousand congregants. Its interior employed what is called the "auditory" form; that is, it was designed as one large hall seating as many people as possible within range of the preacher's voice, the sermon being the most important part of the service in that period. The galleries around three sides of the nave were included for this purpose. Like other Protestant denominations, the original design had a central pulpit with a lectern or reading desk immediately below it. Below that was a "Holy Table" for the communion service, an altar being considered Catholic.
During the second half of the 19th Century, a movement in both Britain and America to return more ceremony and ritual to the services was responsible for the one significant architectural modification of St. Paul's interior. In 1890, the center pulpit was removed and replaced by the present brass pulpit on the chancel's east side and the brass lectern opposite. The chancel itself was extended some 14 feet to accommodate the choir as well as a new marble altar and marble communion rail. The altar reredos, a Tiffany mosaic copy of Leonardo da Vinci's The Last Supper, was added in 1896. The original chancel columns were reused but spaced further apart. Also, beginning in 1890 the original clear-glass windows were removed and replaced with stained-glass memorial windows, a program which continued into the 1920's. Three additional windows from Monumental Church were added in the 1990's when the chancel organ was removed. Also in the 1990's, the choir pews were removed from the chancel and the choir was relocated to the rear gallery.
Dominating the rear gallery is the interior's most recent addition, the Manuel Rosales pipe organ, dedicated in 1998. Its Greek Revival-style case was designed by Philadelphia architect John Blatteau, and uses ornaments published in Minard Lafever's pattern book. Blatteau also designed the Grecian-style communion table.
Connected to the west side of the church by an Ionic colonnade is the parish house, designed by the Richmond firm of Baskervill & Son and completed in 1961. The parish house is in a modified Greek Revival style to harmonize with the church. A multi-level parking deck was incorporated in its design. The colonnade frames the Church's Memorial Garden, a lushly planted courtyard featuring a three-tiered Victorian-style cast-iron fountain.