The former Department of Primary Industries building, finished in unpainted render and painted brickwork, is built on a steeply sloping site with two storeys and basement fronting William Street and a lower three-storeyed wing at the rear fronting Queen's Wharf Road. with a hipped rib and pan galvanised iron roof.

The building was originally built as an Immigration Depot, and construction began in 1865 and completed in 1866.

The building was constructed on part of the former Commandant's Garden. The garden had been part of an attempt to establish some principles of behaviour at Penal Settlements throughout the Colony of New South Wales by the introduction of a Code of Regulations by Governor Darling which, amongst other things, entitled the Commandant to four acres of garden to be tended by up to three gardeners.

A wharf had been constructed c.1825 in front of the adjacent Commissariat Stores [600176] and was originally known as King's Wharf, until 1837 when it became Queen's Wharf after the ascendancy of Queen Victoria. Queen's Wharf was the point of disembarkation of immigrants to the free colony from 1848 to 1897.

Successive colonial governments actively pursued a programme of immigration of free settlers after the Penal Settlement had closed down. The first immigrants to come direct from overseas arrived on 15 December 1848 on the barque Artemisia. The first immigrants were housed temporarily in the Old Military Barracks which were located where the former Treasury Building [600143] now stands. By the 1860s the barracks had deteriorated to such an extent that they were described in the local press as wretched and dilapidated hovels... repugnant and harrowing and an abominable shed. The decision was made to erect a new facility, and the site was selected being a short distance from Queen's Wharf.

Construction began in 1865 and completed in 1866. Designed by the office of Queensland's first Colonial Architect, Charles Tiffin, the building was originally single-storeyed with basement to William Street with a three-storeyed wing at the rear. The rear wing contained three large separate wards, each 57 feet by 32 feet; one for single women at the William Street level, with married couples at the basement level and single men at the sub-basement level, which was also ground level at the rear. To each of these wards was attached a kitchen and bathroom, each on opposite sides. Earth closets were incorporated in a timber structure attached to the southwest of the building, and each ward had a separate entrance from the street. There were also residences for the matron and wardsman, and two rooms for the use of clerks and the Immigration Board in the William Street section. The sanitary arrangements were extensive, with a 2,500 gallon tank supplying water to the whole of the building through lead pipes, with a condensing apparatus in operation at the river which pumped water to the building to supplement the supply of rain water. A luggage room was located on the nearby wharf, as immigrants were not allowed to take baggage into the depot.

The building had a hipped slate roof, unpainted brick walls, and footings of porphyry on weathered rock, and the rear section to Queen's Wharf had internal timber posts and beams supporting timber floor joists. The contractor was Mr J Petrie, and plumbers were Messrs Stewart and Watson. The original estimate was £3,800, but it was likely to have exceeded this estimate by several hundred pounds due to the construction of a substantial fence around the property, as well as a washing shed and luggage room.

In December 1887, a new Immigration Depot at Kangaroo Point opened, and the William Street depot acted as a back-up facility until 1889. The ground floor was still being used in January 1890 as a ward for old men.

In 1890 the building was adapted to form the first offices for the newly established Department of Agriculture. The Department was created in 1887, one of a number of steps taken in the expansion of the role of government during the late 1880s and 1890s, and in 1904 became the Department of Agriculture and Stock, and in 1963 became the Department of Primary Industries. From 1890 onwards the old Immigration Depot was progressively altered and extended to accommodate offices and laboratories primarily for the Department of Agriculture and Stock, and subsequently for other government departments.

By December 1890 the Museum of Economic Botany was accommodated within the building. The following year the Minister of Agriculture was accommodated in the former Immigration Depot. The Minister appears to have been housed in the location previously occupied by the museum, at the rear of the building on the ground floor and the museum was relocated in 1893 to the basement (formerly single men's quarters). This area was partitioned, bunks were removed and a five foot high dado of vertically jointed pine was formed.

In 1897 the Stock Branch of the Colonial Secretary's Department was transferred to the Ministry of Agriculture. In 1898 tenders were called for extensions to the building, including two additional wings at either end and an extra storey to the William Street elevation. The extensions were designed by Thomas Pye, chief draftsman and assistant architect, and John Murdoch, draftsman and assistant architect, under Government Architect Alfred Brady. The form, scale and details of the alterations became the model for all subsequent additions. The tender by Caskie and Thompson was accepted. The extension was of load-bearing cavity brick set in lime-based mortar, with timber floors, and timber roof framing sheeted in galvanised iron rib and pan tiles. External walls were unpainted cement render, and internal walls plastered. The work included the installation of a central skylight in the rear section, and pressed metal ceilings and timber partitions were installed on the ground level of the rear section pre-1916. A toilet block containing earth closets with a nightman's stair was also constructed in 1899.

These extensions reflect the expansion of the Department at this time, particularly the growth in accommodation for entomologists and plant pathologists, as this area of plant science was to continue to expand in response to Queensland's growth in primary production.

In 1900 criticisms of plasterwork (specifically the external rendering over old brickwork to form quoins) led to a royal Commission of Inquiry. Remedial work was subsequently carried out in 1906. Prior to 1915, the southern doorway over the lightwell to William Street was enclosed and replaced with a sash window. In 1916 a new wing was constructed to the south (demolished 1994), consisting of foundation, basement, ground and first floor. This extension accommodated the Agricultural Chemical Laboratory, Entomology and Plant Pathology branches. It was built by day labour, and was intended to form the northwest wing of a new building, with the intention being to demolish the earlier sections of the building. Further extensions to the building were carried out in 1923, 1929, 1935 and 1936.

In 1922 a new staircase was added between the front and rear sections of the building, and the toilet block was reworked in 1924 to replace the original earth closets with water closets.

In 1940 a connection was made between the old photographic studio and the storeroom, and in 1944 the photographic studio suffered major damage by fire. The vertically jointed timber boarding to the rear verandahs was removed C.1951 and replaced with fibrous cement sheeting. Due to the confined nature of the area, a gradual drift from the site began in the 1950s, with the Department of Primary Industries vacating the building in 1989. In 1994 the post-1899 extensions were demolished to make way for a proposed new government office complex.