Section 67 of the Electoral Act 1907 requires the Speaker to issue a writ for a by-election to fill the vacancy.
[2] The member: Additional reasons not within Section 38 include death, resignation, or the voiding of results by a Court of Disputed Returns.
[4] 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.
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.