The Portarlington Steam Flour Mill Company was formed in July 1856 and the Mill, a four storey rectangular plan stone structure, was designed by Andrew McWiliams, a Geelong architect/surveyor, and opened in 1857. A stone house and four weatherboard cottages were also erected on the western corner of the property. The mill closed in 1874 and the original builder, T.H. Widdcombe, established a brickworks on the premises.
The Portarlington Flour Mill is one of the most distinctive flour mill buildings in Victoria constructed at a time when the Bellarine Peninsula was known as the "granary of the colony". Built of local sandstone, regularly fenestrated and with string courses marking each floor, the mill, although a utilitarian structure and unadorned, is a notable work of architect Andrew McWilliams. The mill was for many years the hub of industry in Portarlington and a landmark in the region. The Portarlington Flour Mill has been restored by the National Trust of Australia (Victoria) and is maintained in excellent condition but without the original milling equipment installed.
The boiler house wing was demolished at an unknown date.