The list of Western Australia state by-elections includes every by-election held in the Australian state of Western Australia. By-elections occur whenever there is a vacancy in the Legislative Assembly (or, historically, the Legislative Council), although an imminent state election may allow the vacancy to remain until the dissolution of parliament. Section 67 of the Electoral Act 1907 requires the Speaker to issue a writ for a by-election to fill the vacancy. This can either take place after a resolution of the House if Parliament is in session, or simply upon the cause being established by the Speaker acting alone if the Parliament is in adjournment for more than seven days.

Causes

A by-election occurs whenever there is a vacancy in the Legislative Assembly. Vacancies can occur for the following reasons, according to Section 38 of the Constitution Acts Amendment Act 1899. The member: Additional reasons not within Section 38 include death, resignation, or the voiding of results by a Court of Disputed Returns. The last time a by-election took place for this reason was in 1983, when Gavan Troy, the Labor candidate, narrowly defeated incumbent Liberal member Tom Herzfeld in Mundaring. The seat was won by Troy by a larger margin at the resulting by-election.

Ministerial by-elections

Until a constitutional amendment in 1947, it was necessary for members who were appointed as a minister to resign their seat and contest their seat at a ministerial by-election. This was because the ministers became members of the executive council, which reported to the governor of Western Australia and was therefore deemed an "office of profit" under the Crown. Most ministerial by-elections were a formality with the minister being re-elected unopposed, but on two occasions, in 1901 and 1917, ministers were defeated at the by-elections, in the former case directly causing the fall of the Morgans Ministry.

List of Legislative Assembly by-elections

2020–2029

2010–2019

2000–2009

1990–1999

1980–1989

1970–1979

1960–1969

1950–1959

† Won by acclamation; this date is the date of the return of the writ.

1940–1949

1930–1939

† Won by acclamation; this date is the date of the return of the writ.

1920–1929

† Won by acclamation; this date is the date of the return of the writ.

1910–1919

† Won by acclamation; this date is the date of the return of the writ.

1900–1909

† Won by acclamation; this date is the date of the return of the writ.

1890–1899

† Won by acclamation; this date is the date of the return of the writ. †† This was the date which the writ was issued – the date of the event which caused the by-election is unknown.

Ministerial by-elections

The following ministers had to resign their seats and recontest them at a ministerial by-election. Most were unopposed; these are noted in italics in the table.

List of Legislative Council vacancies