Obviously the best known parts of Parliament - and the reason for its existence - are the Houses and their debating Chambers. New South Wales is a bicameral parliament (consisting of two houses). New South Wales' two houses - the Legislative Council (or Upper House) and Legislative Assembly (or Lower House) consist of Members of Parliament directly elected by the citizens of the state.

However, the building is a complex, really of several buildings, some parts of major heritage importance, other parts of which are more contemporary. Most of the public area is close to the historic Macquarie Street facade. Apart from the two Chambers and their heritage foyer areas, there is also the 1816 Rum Hospital which makes up the central colonnaded section of the Macquarie Street frontage, and the Jubilee Room - the former Parliamentary Library reading room - now used for committee meetings and many public functions. Additions to the public areas from the 1970s include the Fountain Court, with its central fountain by Robert Woodward, and a 175 seat Theatrette directly below. The public area also has a small post office.

Beyond the public areas, a 12-storey building includes dining facilities, Members' and other staff offices, the Parliamentary Library, more meeting rooms, a fitness area, car parking and service areas. Parliamentary staff occupy part of this area (see People in Parliament). There is also a roof garden above the Fountain Court area, sometimes used for functions.

Not so visible are the modern office systems and technology which any contemporary organisation requires. Even the designers of the newer sections of Parliament House in the 1970s could have no concept of the hundreds of personal computers and ancillary equipment; copiers, fax machines and printing technology; servers and extensive networks connected not only by kilometres of cabling within the building but by phone and data networks to all 93 electorate offices across the state.

The building's plant also includes a major power co-generation unit which supplies energy not only to Parliament House but also to the adjoining Sydney Hospital and State Library.