This is a Neoclassical style building that was once Saint Spirit convent. At that time the government used to hold meetings in the convent´s church, but in 1834 they voted to construct a new building for Parliamentary sessions.  Until construction was finished, government sessions were moved to the Royal Theater ballroom. The new building was finally opened in 1850 by Queen Isabel II.

In 1980 it was extended by adding a new building through an original bridge over Floridablanca Street.

The Neoclassical facade features 6 Corinthian style columns, over which there is a triangular frontal piece with a relief that represents Spain and its constitutional law. On either side are allegories of Strength, Justice, Science, Harmony, Agriculture, Trade, River, Peace, and Art.

The monumental steps are protected by two enormous lions, known as Daoiz and Velarde, the two heroes of the Spanish war of independence from France. The lions were melted with bronze captured from the enemy in the war of Africa in 1860. The bronze gates are only opened when the King makes the officially inaugurates Parliament every year. Usually politicians go into the building through the side gates.

The session hall displays a large tapestry with the national coat of arms, and two statues of the Catholic Kings on the sides. The vault is decorated with a painting of Queen Isabel II and is surrounded by three historically important Spaniards: El Cid, Columbus, and Cervantes, author of Don Quixote.