| Country: | Victoria |
| Type: | parliamentary |
| Ongoing: | no |
| Previous Election: | 2006 Victorian state election |
| Previous Year: | 2006 |
| Next Election: | 2010 Victorian state election |
| Next Year: | 2010 |
| Election Date: | 15 September 2007 |
| Seats For Election: | Electoral district of Williamstown in the Victorian Legislative Assembly |
| Registered: | 38,034 |
| Turnout: | 84.93% (6.86) |
| Candidate1: | Wade Noonan |
| Party1: | Australian Labor Party (Victorian Branch) |
| Popular Vote1: | 16,775 |
| Percentage1: | 55.74% |
| Swing1: | 5.96 |
| Candidate2: | Janet Rice |
| Party2: | Australian Greens Victoria |
| Popular Vote2: | 6,592 |
| Percentage2: | 21.90% |
| Swing2: | 9.54 |
| Image3: | IND |
| Party3: | Independent politician |
| Popular Vote3: | 2,703 |
| Percentage3: | 8.98% |
| Swing3: | 8.98 |
| 1Blank: | 2CP |
| 2Blank: | 2CP swing |
| 1Data1: | 64.10% |
| 2Data1: | 10.20 |
| 1Data2: | 35.90% |
| 2Data2: | 35.90 |
| MP | |
| Before Election: | Steve Bracks |
| Before Party: | Labor |
| After Election: | Wade Noonan |
| After Party: | Labor |
The 2007 Williamstown state by-election was held on 15 September 2007 to elect the next member for Williamstown in the Victorian Legislative Assembly, following the resignation of sitting MP and former premier Steve Bracks on 30 July 2007.
Bracks had held the seat since 1994, and had been leader of the state Labor Party since 1999, serving as Premier from 1999 to 2007. Williamstown is generally considered a safe seat for the ALP, and Bracks' predecessor in the seat, Joan Kirner, was also a former Premier.
With the resignation of Premier Steve Bracks on 30 July 2007, a by-election was required. On 4 August 2007 Janet Rice was confirmed to be the candidate for The Greens; the previous day (3 August 2007) the Liberal Party had confirmed that they would not run a candidate.[1] This left Janet Rice as the person most likely to displace an ALP candidate, although she would need to greatly improve upon the vote that the Greens received in the 2006 state election. Former Transport Workers Union of Australia assistant secretary Wade Noonan held the seat for Labor.[2]