In 1969, Government architects were asked to investigate and report on the feasibility and cost of constructing a new Parliamentary Annexe to relieve inadequate accommodation conditions at Parliament House. Three years later, Cabinet directed the State Works Department to review the accommodation requirements at Parliament House in conjunction with the Parliamentary Buildings Committee and develop sketch proposals for a new building. It was proposed that a new building be constructed to include live-in accommodation for country Members and Ministers, individual office facilities for all Members, upgraded library facilities, new dining and function rooms, and a temporary Legislative Assembly Chamber. It was suggested that this building, to become known as the Parliamentary Annexe, be erected on site behind the main building and that the two buildings be linked, incorporating a square green as was originally proposed by Tiffin in 1864. This green has become known as the Speaker's Green and is used for ceremonial purposes.
Tenders for the Annexe were called in August 1975, with construction commencing soon after. Upon its completion in March 1979, the building consisted of two basements, a four-storey podium complex, surmounted by an 18-storey tower block. Although estimates vary, the final cost of the Annexe was approximately $20 million.
The construction of the Annexe was the first major expansion of the parliamentary precinct since the completion of the Alice Street wing in 1891. A major refurbishment of the Annexe was undertaken in 2000.