The ground floor of the state capitol was built in the Classical/Romanesque style. The central open court is dominated by a shaft intended to support a massive dome. The dome and tower were never completed, as it was found that the weight of the building was already causing stress fractures and actually to make the building shift downhill toward State Street. To stop this movement, a very large, 166-foot (51 m) long exterior Eastern Staircase was added to support the front facade. The Capitol exterior is made of white granite from Hallowell, Maine, and the building incorporates Westchester marble cut by state prisoners at Sing Sing. The granite structure is 220 feet (67 m) tall at its highest point, and it is one of eleven U.S. state capitols that does not have a domed roof.

The Capitol initially featured two large murals by Boston artist William Morris Hunt painted directly onto the sandstone walls of the Assembly Chamber. The two enormous works, named The Flight of Night and The Discoverer, each some 45-feet long, were later covered when the Assembly's vaulted ceiling proved unstable and the ceiling was lowered four feet below the murals.