The old windmill is an 1820s convict built structure. There is no record of who ordered its construction or when, but it was known to be operating by late 1828. A treadmill formerly attached to the windmill was used in calmer weather and when the windmill was needing repair. The initial purpose was to grind flour, but the treadmill was also used for punishment. During the convict era two Aborigines were hanged on Windmill Hill, apparently from a window above the perimeter platform. In the late 1830s the miller was Martin Frawley, who still operated the mill for the free settlement in 1845 as an ex-convict. The government put the windmill up for auction in 1849, but such was the local outcry that it was retained as a landmark for public use. It was converted to a signal station in 1861.
The architect was Charles Tiffin and the work was carried out by John Petrie, the prominent contractor and mayor of Brisbane, who replaced the rotating cap and arms and added a fifth floor. A flagstaff was erected in 1865 for flying shipping signals received by telegraph from Fort Lytton. The 1 pm time ball was replaced in 1866 by a time gun and the present time ball, installed in 1894, which was dropped until the mid 1950s. During the 1890s the roof was used by the fire brigade for night fire-spotting. From 1922 to 1926 the tower served the Institute of Radio Engineers for meetings and experiments, and during the 1930s and 1940s it was the venue for pioneer television broadcasting.