The architectural competition which was held in 1924 was won by the firm of Borg–Sirén–Åberg with a proposal called Oratoribus (Latin for "for the speakers").

[1] Johan Sigfrid Sirén (1889–1961), who was mainly responsible for preparing the proposal, was given the task of designing Parliament House.

[3][4][5] On September 25, 2024, the Finnish Extinction Rebellion and Swedish Återställ Våtmarker sprayed red paint on the pillars of Parliament House as a protest against the coal-industry.

[6] Sirén designed Parliament House in a stripped classical architectural style, combining Neoclassicism with early twentieth century modernism.

Sirén's combination of simplified columns and balusters with uncomplicated planar geometry bears comparison to similar explorations by Erik Gunnar Asplund and Jože Plečnik.

The façade is lined by fourteen columns with Corinthian capitals, all made from red granite from Kalvola.

[1] The third floor includes facilities for the information unit and the media, and provides direct access to the press gallery of the plenary chamber.