The Chief Secretary's Building (originally and still commonly known as the Colonial Secretary's Building) is a heritage-listed state government administration building of the Victorian Free Classical architectural style located at 121 Macquarie Street, 65 Bridge Street, and at 44–50 Phillip Street in the Sydney central business district of New South Wales, Australia. The ornate five-storey public building was designed by Colonial Architect James Barnet and built in two stages, the first stages being levels one to four completed between 1873 and 1881, with Walter Liberty Vernon completing the second stage between 1894 and 1896 when the mansard at level five and the dome were added.
The sandstone building was the seat of colonial administration, has been used continuously by the Government of New South Wales, and even today holds the office of the Governor of New South Wales. Its main occupant is the Industrial Relations Commission of New South Wales; several of the larger rooms are now courtrooms.