Governor Macquarie had a problem with the streets. Convict men, allowed to find their own lodgings after the day's work, spent their evenings in ways the governor found disturbing, and he became convinced that proper barracks would improve their conduct and their productivity. He asked Greenway for a building to house six hundred men, the foundation stone was laid on 6 April 1817, and convict labour raised the walls. Macquarie opened it on 20 May 1819 with ceremony and a feast for the prisoners. The reality inside was hard. Four rooms on each floor were strung with two rows of hammocks just over two feet apart, the long eastern rooms sleeping seventy men each. Designed for six hundred, the barracks at times held as many as fourteen hundred. The commissioner sent to review the colony, John Bigge, complained that packing so many "depraved and desperate characters" together had merely concentrated the problem rather than solving it.

Life in the barracks was not simple captivity. The convicts worked for the government during the week but were permitted to labour for their own benefit on Saturdays, a privilege Macquarie watched jealously and did not like to see abused. The system had a peculiar logic. Men who behaved could earn the reward of living outside the walls; men caught gambling, drunk, brawling, or merely loitering on a Saturday had that freedom revoked and were sent back inside. Confinement to the barracks became, in effect, a punishment in its own right. The mixed response of the convicts themselves tells you something honest about the place. Some who could afford their own lodgings resented being shut in; others, with no roof of their own, were glad of one. These were real men navigating a strange machine of control, finding what room they could inside it, neither the hardened villains of colonial rhetoric nor passive victims, but people making the best of a narrow set of choices.

The convict era ended, and the building found a gentler, sadder purpose. From 1848 it became an immigration depot for women, and through its doors passed an estimated forty thousand immigrant women over thirty-eight years, some with their children, seeking shelter and a foothold in a new country. Among the first were more than two thousand orphan girls who had survived the Great Irish Famine, sent across the world carrying grief and hunger and a fragile hope of something better. Their presence is now marked at the site by the Australian Monument to the Great Irish Famine, which the artists called An Gorta Mor, "The Great Hunger." It includes a bare metal table set with a single dinner plate, jutting from the wall at an angle, an image of want that needs no caption. A building raised to discipline transported men became, in its second life, a place for the friendless and the dispossessed to begin again.

After the women came the lawyers. The barracks was carved up to house a bewildering succession of courts and offices, the District Court, the Coroner, bankruptcy and probate and industrial tribunals, each leaving its mark on the joinery and the staircases as the building was adapted again and again. Yet through every alteration, the essence of Greenway's design survived. Its restraint still shows in the pedimented front, the simple piers, the distinctive double string course beneath the eaves, and the clock above, inscribed for the governor who built it. Since the 1980s, archaeologists have read the site like a manuscript, and the building reopened in 2020 after an eighteen-million-dollar restoration as an immersive museum. Its deepest value lies in its honesty. Hyde Park Barracks preserves a clear-eyed record of how a penal colony housed and managed the people it transported, a turning point in colonial control, and in 2010 UNESCO inscribed it among the Australian Convict Sites as one of the best surviving witnesses to that history.