The Green Room was originally the senators' cloakroom. Before the renovation in the early 20th century, senators would finalize their speeches here, read or do study work. Today, they have their own office in the Parliamentarians' House for that purpose.

The Parliamentarians' House is housed in the building of the former Ministry of Railways, Post, Telegraphy and Navigation, which was built between 1889 and 1892 under the direction of architect Henri Beyaert in a neo Flemish Renaissance style. The Senate and the House of Representatives bought it together at the end of the 1970s. It was inaugurated in 1987.

The wings house the individual offices of the federal members of parliament and their assistants, a number of meeting rooms and other facilities such as the staff restaurant.