This building, completed in 1931 by the architects Eduard Le Monnier and Héctor Ayerza, was inspired by the 18th century French neoclassical style. The building houses a library and newspaper archive that are open to the public, as well as its three halls and the legislative chamber.
The 97-metre tower features a Westminster clock with four 4.5 diametre faces. The clock is connected to five bells named La Santa María, La Pinta, La Niña, La Porteña and La Argentina. The largest weighs 1.8 tons. A carrillon of 30 bells weighing 27 tons can be used to play melodies using a wooden keyboard located in the tower.