Casual vacancies in the House of Representatives are filled by by-elections, which may occur when a member of the House of Representatives dies, resigns or for some other reason. When a member of the House of Representatives resigns, he or she would normally tender the resignation to the Speaker. The Speaker has a discretion as to when to call a by-election and may not call one at all, for example, if a general election is imminent. At least 33 days must elapse between the issue by the Speaker of a writ and the date of a by-election, and the Speaker cannot issue the writ until receipt of a formal letter of resignation. A by-election must take place on a Saturday.
Brackets around a date indicate that the candidate was unopposed when nominations closed. These candidates were declared "elected unopposed" with effect from the date of the closing of nominations, and there was no need to hold a by-election.