2023 Rockingham state by-election

A by-election for the electoral district of Rockingham in Western Australia was held on 29 July 2023, following the resignation of Premier and sitting Labor MP Mark McGowan, on 8 June 2023. The writ was issued on the same day.

The two major party candidates for the election were Magenta Marshall for the Australian Labor Party and Peter Hudson for the Liberal Party. Additionally, Hayley Edwards the Deputy Mayor of the City of Rockingham also announced her candidacy. The Greens preselected Madeleine De Jong. There were nine candidates for the seat. Notably, both major parties preselected candidates under the age of 30.

The election was called for Labor at 7:30pm AWST, with Marshall claiming victory for the Labor Party. However, Labor suffered one of the biggest swings against it at a by-election in the state's history: with a swing against them of 33.4% in the primary vote and a swing against of 22.5% in the two-party-preferred vote.

Resignation of Mark McGowan
On 29 May 2023, McGowan announced that he was resigning as Premier of Western Australia and the MLA for Rockingham, a seat he had held since 1996. He stated that the job was "relentless" and that he no longer had the "energy or drive to continue". Reflecting on his political career, McGowan thanked voters of Western Australia who had "provided [him] with the opportunity of a lifetime." McGowan led Labor to government for the first time since 2008 in 2017.

Seat details
The electoral district of Rockingham was first contested at the 1974 Western Australian state election and has been held by the Australian Labor Party since its inception. Previous member Mike Barnett held the district from the beginning until his retirement at the 1996 election where he was succeeded by McGowan. Barring the elections in 1974 and 1977, Rockingham has been a consistently safe electorate for Labor with the smallest margin being 0.9 per cent of the two-party-preferred vote (TPP) in its first election. At the 2021 Western Australian state election, McGowan received a TPP of 87.7% - one of the highest margins in both federal and state elections in Australia.

Geographically, the district encompasses the City of Rockingham and its surrounding areas. Located 47 km south-southwest of the Perth CBD by the coast near the Cockburn Sound inlet. The district is adjacent to several maritime and resource-industry installations and offshore is home to Australia's largest naval fleet and submarine base at Garden Island. According to the 2021 Census, the median age of Rockingham is 45 with a weekly median household income of $1,273 per week. 20.5 per cent of residents are currently engaged in secondary education and 17.7 per cent in tertiary education.

Labor
On 14 June, it was confirmed that Labor strategist Magenta Marshall has been preselected for Labor to run as the party's candidate in Rockingham.

Liberal
On 13 June, the Liberal Party announced that the party would contest the by-election.

On 18 June, it was reported that 21-year-old Peter Hudson will be the party's candidate. He was the only person to nominate for preselection.