The OEH supported the community, business and government in protecting, strengthening and making the most of a healthy environment and economy within the state.

The department was headed by Director-General Lisa Corbyn and headquartered in Sydney, with offices across the city and state.

The Office consists of seven functional areas: Although an agency of the Government of New South Wales, the Office includes a number of independent boards and committees; for example, the management of the Botanic Gardens is overseen by the Botanic Gardens Trust, and the powers of the Environment Protection Authority, as exercised by the Authority to investigate or prosecute government agencies, are formally vested in an independent board.

It carries out environmental protection work in a variety of areas including air and water quality, environmental incident management, contaminated land, noise, coal seam gas, native forestry, dangerous goods, hazardous waste, chemicals and pesticides, and waste and resource recovery.

With the national parks estate covering around 10 per cent of New South Wales, the department is a significant player in debates over land management in the state.

The NPWS has a significant amount of responsibility for fire management in the state, and is often the target of criticism when Sydney – the so-called "city in a national park" – is threatened by bushfire.

The Carr Labor government sought to significantly increase the size of the national parks estate.