The Callan Park (Special Provisions) Act, 2002 (NSW) restricts future uses of the site to health, tertiary education and community uses.

[6][7] Before European settlement the Wangal clan or band lived at the site and their territory extended along the Parramatta River from about Petersham westward.

Due to a smallpox epidemic between 1789 and 1790 and European land development, only about 50 people from Dharug families were living in the Sydney area by 1900.

A contemporary description of the estate noted its "stately wrought iron gates, unequalled in the colony, supported on handsome pillars each one a block of stone with pedestal and cap, and a beautiful serpentine approach, the avenue lined with trees and choice shrubs, 1/8 of a mile long".

Colonial Architect James Barnet worked with the Inspector of the Insane, Dr Frederick Norton Manning to produce a group of twenty neo-classical buildings, considerably extending the asylum operating out of the original house.

[11][6] During World War I changes to mental health care were instigated and in 1914 patients could only be treated if they were committed into one of the major institutions, resulting in additional facilities being built in the grounds.

After twelve months at Royal Prince Alfred Hospital, Bailey became a medical officer at Broughton Hall Psychiatric Clinic, Leichhardt, in 1952.

He had already come under the influence of such prominent advocates of surgical and pharmacological treatments for mental illness as (Sir) William Trethowan and Cedric Swanton.

From December 1954 he spent fifteen months on a World Health Organisation fellowship in the United States of America and Europe, closely observing the sedation techniques, psychosurgery and electroconvulsive therapy methods of Ewan Cameron in Canada, William Sargant in London and Lars Leksell in Sweden.

[6] The Kirkbride complex continued to be used for the housing and treatment of patients until 1994, when the last remaining services were transferred to other buildings in the Callan Park grounds, towards the Broughton Hall at the southern end of the site.

Many patients were also transferred into buildings in the local community, in line with the policy of the State Government (see The Richmond Report of 1983 which accelerated the move towards de-institutionalising care), creating a number of social and moral problems.

In 2007 it was reported that the Minister for Planning, Frank Sartor MP had announced in Parliament that the University of Sydney and the Government had commenced discussions about the future use of Callan Park.

[13] The parklands are currently open to the public for use and enjoyment in accordance with the principal objects of the Callan Park (Special Provisions) Act 2002.

The Callan Park (Special Provisions) Act, 2002 (NSW) restricts future uses of the site to health, tertiary education, and community (not-for-profit).

[15][1] In 2015, the New South Wales Parliament approved the draft masterplan and agreed to establish a specialised trust, finalise the site's master plan and develop a sustainable long-term funding model to protect it.

Garryowen also retains some early plantings, such as an old (1.5m trunk girth) evergreen or Southern magnolia /bull bay, (M.grandiflora) and a Camellia japonica cv.

Four mature jacarandas (J.mimosifolia) and 3 cabbage tree palms (Livistona australis) and a cedar wattle (Acacia elata) are to Garryowen's north.

To the north are a Bunya pine (Araucaria bidwillii), 3 Bhutan cypresses (Cupressus torulosa) and a Norfolk Island hibiscus tree (Lagunaria patersonia.

It shows Lewis' architectural trademarks, such as reeded, rather than fluted mouldings in the tops of window cases, floor skirtings are panelled, French doors onto the verandahs (onto the entrance front (north) and garden front (west) sides of the house (these doors were later changed by James Barnet to hung windows).

The octagonal asphalt paving blocks on the verandah floors are a trademark of James Barnet, also seen at his Police & Justice Museum near Circular Quay and South West Rocks Lighthouse.

It is constructed of rendered brick ashlar coursed single-storey verandah with timber supports and posts, corrugated iron roofed.

Extensive brick additions to the east which have been rendered and painted (1992, Preliminary Heritage & Conservation Register – Central District Area Health Service).

Kirkbride Block is significant as the collaborative work of three prominent figures in the late 19th century, James Barnet, Charles Moore and Frederick Norton Manning, as the largest remaining mental institution in NSW and as the first to be designed as a curative and therapeutic environment.

They are associated with: Dr Frederick Norton Manning, Inspector General for the Insane; James Barnet, Colonial Architect; and Charles Moore, Director of the then Botanic Gardens, Sydney.The building was also listed on the (now defunct) Register of the National Estate.