The Penitentiary House, etc. Act was an Act of the Parliament of the United Kingdom, granted royal assent on 20 April 1812.
It built on the Penitentiary Act 1779 and Penitentiary for Convicts Act 1794, making arrangements to build Millbank prison on a site bought from the Marquis of Salisbury and since 1794 vested in Jeremy Bentham. His plan to build a panopticon of his own design on the site had stalled, though the 1812 Act compensated him for the money he had invested in the scheme.
The new prison was to serve Middlesex and the City of London, specifically those in those two areas who had been convicted of offences liable to penal transportation or of capital crimes - rather than be executed, the Act required the latter to be imprisoned for life at Millbank. The Act set out how it was to be built, run, maintained and overseen, with a maximum capacity of 300 male prisoners and 300 female prisoners.