This is a list of by-elections for the Victorian Legislative Assembly. A by-election may be held when a member's seat becomes vacant through resignation, death or some other reasons. These are referred to as casual vacancies.

• Brackets around a date (D/M/Y) indicate that the candidate was unopposed when nominations closed or that, as a result of an appeal against an election result, the sitting member was replaced by the appellant. These candidates were declared "elected unopposed" with effect from the date of the closing of nominations or appeal decision, and there was no need to hold a by-election.
• By-elections which resulted in a change in party representation are highlighted as: Gains for the Labor Party and its splinter groups in red; for the Liberal Party and its predecessors in blue; for the National Party and its predecessors in green; for the Greens in green and for independents and minor parties in grey.