The Chief Secretary of New South Wales, known from 1821 to 1959 as the Colonial Secretary, was a key political office in state administration in New South Wales, and from 1901, a state in the Commonwealth of Australia. During much of the 19th century, the Colonial Secretary was the pre-eminent figure in public life. The role of the Chief Secretary changed significantly from the time of its creation in 1821 to its final use in 1995, with various responsibilities changing hands. Nominally subordinate to the Governor of New South Wales from the early 19th century until the beginning of full self-government in 1856, he was effectively a government record-keeper and the officer with responsibility for the general administration of the colony. However, for most of its history the Chief Secretary was in charge of all matters relating to correspondence with government departments, naturalisation, the Great Seal, state security, censorship and classification laws, the arts, Public Health, Aboriginal welfare, Lord Howe Island, and environmental protection and fisheries.

The Chief Secretary's Building is a heritage-listed state government administrative 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.