Williamstown is an electoral district of the Legislative Assembly in the Australian state of Victoria. It is a 33 km² urban electorate in the inner south-western suburbs of Melbourne, encompassing the suburbs of Brooklyn, Newport, Spotswood, Williamstown and Yarraville. The electorate had a population of 54,426 as of the 2006 census.
Williamstown is one of only three electorates (along with Brighton and Richmond) to have been contested at every election since 1856. It is a very safe seat for the Australian Labor Party which has held it uninterrupted for over a century. Notable former members include John Lemmon, who held the seat for a Victorian record 51 years until his retirement in 1955, and former Premiers Joan Kirner and Steve Bracks. 
Steve Bracks held the seat from a by-election in 1994 until his surprise resignation on 30 July 2007. A by-election was held on 15 September 2007, resulting in the election of Labor's Wade Noonan.