On February 24, 1918, Estonia became an independent state. Toompea became the seat of the supreme power of the Republic of Estonia, however, in the castle there was no room spacious enough to accommodate the representation of the people. In the course of the February Revolution the convent building had been burnt down, and its ruins seemed suitable for a foundation of a new building.

The building of the Riigikogu was designed by architects Eugen Haberman and Herbert Johanson, and it was inaugurated on September 12, 1922. The two-storeyed and four-winged building surrounds a trapezoid inner court, strictly following the ground plan of the former convent building. Only the southern wing is a little wider. Two different styles are discernible in the architecture of the building: Traditionalism and Expressionism of the 1920s. Both these styles agree well with the buildings at Toompea that were constructed earlier.

The exterior of the house is in the Traditionalistic style (plain exterior, facade with few small openings). The Karelian granite exterior framework of the hall windows is almost like an elaboration of national Romanticism towards Expressionism. Expressionistic motifs are even more dominant inside the house. The lofty hall (it goes through two storeys) in which sittings of the Riigikogu are held is the most outstanding room of the building. The high vaulted and fluted ceiling has been painted lemon yellow. It is separated from the wall by a zigzag cornice which hides lamps. The use of reflected shadeless light coming from a hidden source was very innovative in 1920s. The walls of the sitting chamber are ultramarine, and the jagged door and window jambs are rusty brown.

Furniture is of light birch plywood decorated with contrasting black details. The Riigikogu building is unique among the parliament buildings of the world, since it is the only Expressionistic one in the world.

In 1997, the sitting chamber was restored. Inauguration of the restored chamber took place on September 8, 1997. The author of the general architectural design of the restoration works was Ülar Saar, the interior decoration was by Leila Pärtelpoeg. Historian Mart Kalm consulted the architects in the matters of the history of architecture, colour expertise of the hall was made by the lecturers of the Academy of Arts Kaarel and Mari Kurismaa. Specialist in the technology of restoration Helve Ilves analyzed chemically specimens of paints and, in this way, established the exact composition of the paints used originally in the interior decoration of the hall.

In addition to the restoration of the original colour solution, the windows in the northern wall of the hall were reopened, and the side balcony with a view into the inner court was restored.