The site occupied by El Capitolio was originally an area of swamp which was later used for slave dwellings and later still for the country's first botanical garden. In 1839, after the plants were relocated, the Villanueva Station (Estación de Ferrocarriles de Villanueva) was constructed on the site. The station was inaugurated in 1839 and was in use until the first decade of the 20th century when a modern station was constructed further to the east of the city. Before the existing building was erected there were other construction projects proposed for the site. The first, proposed in 1912, was to build a Presidential Palace, but the idea was later modified to construction of a building for the Cuban legislature. Financing was obtained and the work started in December 1917 but stopped during World War I and was never recommenced. The dome of the building, which had been completed before work was suspended, was destroyed in an explosion in 1918.
In 1925, the dictator Gerardo Machado took power and commissioned a new design from the architects Raúl Otero and Eugenio Raynieri. The previous, partially completed building was demolished and work began on the new building on 1 April 1926. Over seen by the U.S. firm of Purdy and Henderson, 8,000 labourers worked 8-hour shifts 24 hours a day, and as a result the building was completed in just 3 years and 50 days.
The building was named after a referendum on the choice of either the El Palacio del Congreso (Palace of Congress) or El Capitolio, and was inaugurated on 20 May 1929. The legislature did not move into the building until February 1931, as although the structure was complete by 1929 it took almost another two years before the interior decoration was finished. The building is finished with fine marble throughout and the total cost of construction and decoration is estimated to have been 17 million pesos. The building served as the seat of the legislature until the late 1950s; both the House of Representatives and Senate were based in the building. In the 1960s it became home to the Ministry of Science, Technology and the Environment. The main floor (which is on the first storey) is open to visitors and many of the rooms are used to host conferences and meetings.
The cupola, which is stone clad around a steel frame which was constructed in the United States and imported to Cuba, is set forward on the building to allow for some large rooms at the rear, including what is now the National Library of Science and Technology. In the original design the dome was to be decorated with stylised palm leaves but this addition was never executed. At almost 92 m (300 ft) high, the dome was the highest point in the city of Havana until the 1950s (this honour now belongs to the José Martí Memorial).
Around the building are gardens laid out by French landscape architect and designer Jean-Claude Nicolas Forestier at the time of the original construction. Based on the designs of some of the beautiful simple European gardens they consist of areas of lawn bordered by paths and highlighted by palms. Four groups of Royal Palms accent the design.
The 55 steps leading to the main entrance, known as La Escalinata are flanked on either side by 6.5 m (21 ft) statues by the Italian artist Angelo Zanelli. To the left is Work (El Trabajo) and to the right The Tutelary Virtue (La Virtud Tutelar). The steps lead up to the central portico, which is 36 m (118 ft) wide and more than 16 m (52½ ft) tall. There are 12 granite Roman style columns arranged in two rows and each over 14 m (46 ft) tall. Beyond the portico, three large bronze doors with bas-reliefs by Zanelli allow access to the main hall.
The inside of the main hall under the cupola is dominated by the huge Statue of the Republic (La Estatua de la República). The statue, also by Zanelli, was cast in bronze in Rome in three pieces and assembled inside the building after its arrival in Cuba. It is covered with 22 carat (92 %) gold leaf and weighs 49 tons. At 15 m (49¼ ft) tall, it was the second highest statue under cover in the world at the time, with only the Great Buddha of Nara being taller. It was later relegated to third place after the construction of the statue of Abraham Lincoln in the Lincoln Memorial. The statue stands on a plinth 2.5 m (8¼ ft) high bringing the total height to 17.54 m (55¼ ft). A Creole Cuban, Lily Valty served as the model for the body for Zanelli, and the inspiration for the statue came from Athena, the Greek goddess of wisdom.
Embedded in the floor in the centre of the main hall is a replica 25 carat (5 g) diamond, which marks Kilometre Zero for Cuba. The original diamond, said to have belonged to Tsar Nicholas II of Russia and have been sold to the Cuban state by a Turkish merchant, was stolen on 25 March 1946 and mysteriously returned to the President, Ramón Grau San Martín, on 2 June 1946. It was replaced in El Capitolio by a replica in 1973.
To either side of the main hall is the Salón de Pasos Perdidos (Hall of Lost Steps), named for its acoustic properties. These halls, with inlaid marble floors and gilded lamps, lead to the two semicircular chambers that formerly housed the Parliament and Chamber of Deputies. The Parliament chamber to the right of building is backed on to by the President's office which has a door opening directly onto the dias.
A range of different lamps are seen throughout the building. These were all designed specifically for the building by Cuban designers and the majority of them manufactured in France.
In the centre of the building are two patios which provide light and ventilation for the offices of first (ground), third and fourth floors. The north patio features another statue The Rebellious Angel (El Ángel Rebelde) which was donated to the building after the inauguration. There is a small fifth floor, and a sixth floor which gives access only to part of the cupola.