The list of Ontario by-elections includes every by-election held in the Canadian province of Ontario. By-elections occur whenever there is a vacancy in the Legislative Assembly, although an imminent general election may allow the vacancy to remain until the dissolution of parliament.

Causes

A by-election occurs whenever there is a vacancy in the Ontario legislature. Vacancies can occur for the following reasons:

List of Ontario by-elections

Death of a member. Resignation of a member. Voided results Expulsion from the legislature. Ineligibility to sit.

List of Ontario by-elections

When there is a vacancy, a by-election must be called within six months. Under amendments to the Election Act approved in 2016, a by-election is no longer required when a vacancy occurs in the 12 months leading up to a fixed general election date.

List of Ontario by-elections

Ministerial by-elections

The list includes ministerial by-elections which occurred due to the requirement that incumbent members recontest their seats upon being appointed to Cabinet. These by-elections were almost always uncontested. This requirement was amended in 1926 to exempt ministers appointed within three months after a general election. In 1941 it was abolished completely.

43rd Legislative Assembly of Ontario 2022–present

42nd Legislative Assembly of Ontario 2018–2022

41st Legislative Assembly of Ontario 2014–2018

40th Legislative Assembly of Ontario 2011–2014

39th Legislative Assembly of Ontario 2007–2011

38th Legislative Assembly of Ontario 2003–2007

37th Legislative Assembly of Ontario 1999–2003

36th Legislative Assembly of Ontario 1995–1999

35th Legislative Assembly of Ontario 1990–1995

34th Legislative Assembly of Ontario 1987–1990

33rd Legislative Assembly of Ontario 1985–1987

32nd Legislative Assembly of Ontario 1981–1985

31st Legislative Assembly of Ontario 1977–1981

30th Legislative Assembly of Ontario 1975–1977

no by-elections

29th Legislative Assembly of Ontario 1971–1975

28th Legislative Assembly of Ontario 1967–1971

27th Legislative Assembly of Ontario 1963–1967

26th Legislative Assembly of Ontario 1959–1963

25th Legislative Assembly of Ontario 1955–1959

† Won by acclamation

24th Legislative Assembly of Ontario 1951–1955

23rd Legislative Assembly of Ontario 1948–1951

22nd Legislative Assembly of Ontario 1945–1948

21st Legislative Assembly of Ontario 1943–1945

20th Legislative Assembly of Ontario 1937–1943

† Won by acclamation

*Though nominally an "Independent-Liberal", MacBride was a supporter of the Liberal government and was a cabinet minister at the time of his death