# List of Ontario by-elections

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

## 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 2022–2025

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Bay of Quinte | September 19, 2024 | Todd Smith | Progressive Conservative | Tyler Allsopp | Progressive Conservative | Resigned to return to the private sector. | Yes |
| Milton | May 2, 2024 | Parm Gill | Progressive Conservative | Zee Hamid | Progressive Conservative | Resigned to run for a seat in the House of Commons | Yes |
| Lambton—Kent—Middlesex | May 2, 2024 | Monte McNaughton | Progressive Conservative | Steve Pinsonneault | Progressive Conservative | Resigned to return to the private sector | Yes |
| Kitchener Centre | November 30, 2023 | Laura Mae Lindo | New Democratic | Aislinn Clancy | Green | Resigned to take up role at University of Waterloo. | No |
| Scarborough—Guildwood | July 27, 2023 | Mitzie Hunter | Liberal | Andrea Hazell | Liberal | Resigned to run for Mayor of Toronto, lost. | Yes |
| Kanata—Carleton | July 27, 2023 | Merrilee Fullerton | Progressive Conservative | Karen McCrimmon | Liberal | Resigned. | No |
| Hamilton Centre | March 16, 2023 | Andrea Horwath | New Democratic | Sarah Jama | New Democratic | Resigned to run for Mayor of Hamilton, elected. | Yes |

## 42nd Legislative Assembly of Ontario 2018–2022

| By-election | Date | Incumbent | Party | Party | Winner | Party | Party | Cause | Retained |
| Ottawa—Vanier | February 27, 2020 | Nathalie Des Rosiers | | Liberal | Lucille Collard | | Liberal | Resigned to become Principal of Massey College | Yes |
| Orléans | February 27, 2020 | Marie-France Lalonde | | Liberal | Stephen Blais | | Liberal | Resigned to run in the federal district of Orléans; elected. | Yes |

## 41st Legislative Assembly of Ontario 2014–2018

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Sault Ste. Marie | June 1, 2017 | David Orazietti | Liberal | Ross Romano | Progressive Conservative | Resignation. | No |
| Niagara West—Glanbrook | November 17, 2016 | Tim Hudak | Progressive Conservative | Sam Oosterhoff | Progressive Conservative | Resignation to become CEO of Ontario Real Estate Association. | Yes |
| Ottawa—Vanier | November 17, 2016 | Madeleine Meilleur | Liberal | Nathalie Des Rosiers | Liberal | Resignation. | Yes |
| Scarborough—Rouge River | September 1, 2016 | Bas Balkissoon | Liberal | Raymond Cho | Progressive Conservative | Resignation. | No |
| Whitby—Oshawa | February 11, 2016 | Christine Elliott | Progressive Conservative | Lorne Coe | Progressive Conservative | Resigned after losing leadership contest. | Yes |
| Simcoe North | September 3, 2015 | Garfield Dunlop | Progressive Conservative | Patrick Brown | Progressive Conservative | Resignation to create a vacancy for PC leader Brown. | Yes |
| Sudbury | February 5, 2015 | Joe Cimino | New Democratic | Glenn Thibeault | Liberal | Resignation. | No |

## 40th Legislative Assembly of Ontario 2011–2014

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Thornhill | February 13, 2014 | Peter Shurman | Progressive Conservative | Gila Martow | Progressive Conservative | Resignation | Yes |
| Niagara Falls | February 13, 2014 | Kim Craitor | Liberal | Wayne Gates | New Democratic | Resignation | No |
| Scarborough—Guildwood | August 1, 2013 | Margarett Best | Liberal | Mitzie Hunter | Liberal | Resignation | Yes |
| Etobicoke—Lakeshore | August 1, 2013 | Laurel Broten | Liberal | Doug Holyday | Progressive Conservative | Resignation | No |
| Ottawa South | August 1, 2013 | Dalton McGuinty | Liberal | John Fraser | Liberal | Resignation to re-enter private life after retiring as Premier and Liberal leader. | Yes |
| Windsor—Tecumseh | August 1, 2013 | Dwight Duncan | Liberal | Percy Hatfield | New Democratic | Resignation following the retirement of Premier McGuinty | No |
| London West | August 1, 2013 | Chris Bentley | Liberal | Peggy Sattler | New Democratic | Resignation following the retirement of Premier McGuinty | No |
| Kitchener—Waterloo | September 6, 2012 | Elizabeth Witmer | Progressive Conservative | Catherine Fife | New Democratic | Resignation to accept appointment as Chair of the Workplace Safety & Insurance Board | No |
| Vaughan | September 6, 2012 | Greg Sorbara | Liberal | Steven Del Duca | Liberal | Resignation | Yes |

## 39th Legislative Assembly of Ontario 2007–2011

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Ottawa West—Nepean | March 4, 2010 | Jim Watson | Liberal | Bob Chiarelli | Liberal | Resignation to run for Mayor of Ottawa | Yes |
| Leeds—Grenville | March 4, 2010 | Robert Runciman | Progressive Conservative | Steve Clark | Progressive Conservative | Resignation upon appointment to Canadian Senate. | Yes |
| Toronto Centre | February 4, 2010 | George Smitherman | Liberal | Glen Murray | Liberal | Resignation to run for Mayor of Toronto. | Yes |
| St. Paul's | September 17, 2009 | Michael Bryant | Liberal | Eric Hoskins | Liberal | Resignation to accept municipal appointment. | Yes |
| Haliburton—Kawartha Lakes—Brock | March 5, 2009 | Laurie Scott | Progressive Conservative | Rick Johnson | Liberal | Resignation to create vacancy for PC leader John Tory. | No |

## 38th Legislative Assembly of Ontario 2003–2007

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Burlington | February 8, 2007 | Cam Jackson | Progressive Conservative | Joyce Savoline | Progressive Conservative | Resignation to run for Mayor of Burlington | Yes |
| York South—Weston | February 8, 2007 | Joe Cordiano | Liberal | Paul Ferreira | New Democratic | Resignation | No |
| Markham | February 8, 2007 | Tony Wong | Liberal | Michael Chan | Liberal | Resignation to run municipally. | Yes |
| Parkdale—High Park | September 14, 2006 | Gerard Kennedy | Liberal | Cheri DiNovo | New Democratic | Resignation to seek federal Liberal leadership. | No |
| Whitby—Ajax | March 30, 2006 | Jim Flaherty | Progressive Conservative | Christine Elliott | Progressive Conservative | Resignation to run federally. | Yes |
| Toronto—Danforth | March 26, 2006 | Marilyn Churley | New Democratic | Peter Tabuns | New Democratic | Resignation to run federally. | Yes |
| Nepean—Carleton | March 26, 2006 | John Baird | Progressive Conservative | Lisa MacLeod | Progressive Conservative | Resignation to run federally. | Yes |
| Scarborough—Rouge River | November 24, 2005 | Alvin Curling | Liberal | Bas Balkissoon | Liberal | Resignation to accept diplomatic posting. | Yes |
| Dufferin—Peel—Wellington—Grey | March 17, 2005 | Ernie Eves | Progressive Conservative | John Tory | Progressive Conservative | Resignation. | Yes |
| Hamilton East | May 13, 2004 | Dominic Agostino | Liberal | Andrea Horwath | New Democratic | Death | No |

## 37th Legislative Assembly of Ontario 1999–2003

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Dufferin—Peel—Wellington—Grey | May 2, 2002 | David Tilson | Progressive Conservative | Ernie Eves | Progressive Conservative | Resignation to create vacancy for PC leader and Premier Ernie Eves. | Yes |
| Nipissing | May 2, 2002 | Mike Harris | Progressive Conservative | Al McDonald | Progressive Conservative | Resignation after retiring as Premier and party leader. | Yes |
| Beaches-East York | September 20, 2001 | Frances Lankin | New Democratic | Michael Prue | New Democratic | Resignation to become CEO of United Way Toronto | Yes |
| Vaughan—King—Aurora | June 28, 2001 | Al Palladini | Progressive Conservative | Greg Sorbara | Liberal | Death | No |
| Parry Sound—Muskoka | March 22, 2001 | Ernie Eves | Progressive Conservative | Norm Miller | Progressive Conservative | Resignation | Yes |
| Wentworth-Burlington | September 7, 2000 | Toni Skarica | Progressive Conservative | Ted McMeekin | Liberal | Resignation to protest municipal amalgamation. | No |

## 36th Legislative Assembly of Ontario 1995–1999

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Nickel Belt | October 1, 1998 | Floyd Laughren | New Democratic | Blain Morin | New Democratic | Resignation to accept appointment as chair of Ontario Energy Board | Yes |
| Oriole | September 4, 1997 | Elinor Caplan | Liberal | David Caplan | Liberal | Resignation to enter federal politics | Yes |
| Ottawa West | September 4, 1997 | Bob Chiarelli | Liberal | Alex Cullen | Liberal | Resignation to run municipally | Yes |
| Windsor—Riverside | September 4, 1997 | Dave Cooke | New Democratic | Wayne Lessard | New Democratic | Resignation to accept provincial appointment to the Education Improvement Commission. | Yes |
| York South | May 23, 1996 | Bob Rae | New Democratic | Gerard Kennedy | Liberal | Resignation. | No |

## 35th Legislative Assembly of Ontario 1990–1995

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Victoria—Haliburton | March 17, 1994 | Dennis Drainville | Independent | Chris Hodgson | Progressive Conservative | Resignation to run federally. | No |
| Essex South | December 2, 1993 | Remo Mancini | Liberal | Bruce Crozier | Liberal | Resignation | Yes |
| St. George—St. David | April 1, 1993 | Ian Scott | Liberal | Tim Murphy | Liberal | Resignation | Yes |
| Don Mills | April 1, 1993 | Margery Ward | New Democratic | David Johnson | Progressive Conservative | Death | No |
| Brant—Haldimand | March 5, 1992 | Robert Nixon | Liberal | Ronald Eddy | Liberal | Resignation to accept federal appointment. | Yes |

## 34th Legislative Assembly of Ontario 1987–1990

| By-election | Date | Incumbent | Party | Party | Winner | Party | Party | Cause | Retained |
| Welland—Thorold | November 3, 1988 | Mel Swart | | New Democratic | Peter Kormos | | New Democratic | Resignation. | Yes |
| London North | March 31, 1988 | Ron Van Horne | | Liberal | Dianne Cunningham | | Progressive Conservative | Resignation. | No |

## 33rd Legislative Assembly of Ontario 1985–1987

| By-election | Date | Incumbent | Party | Party | Winner | Party | Party | Cause | Retained |
| Cochrane North | August 14, 1986 | René Fontaine | | Liberal | René Fontaine | | Liberal | Resignation from cabinet and legislature to resubmit candidacy to voters after it was revealed he had forgotten to disclose his ownership of shares in a mining company contrary to conflict of interest guidelines. | Yes |
| York East | April 17, 1986 | Robert Elgie | | Progressive Conservative | Christine Hart | | Liberal | Resignation to accept appointment as head of Workers Compensation Board. | No |

## 32nd Legislative Assembly of Ontario 1981–1985

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Wentworth North | December 13, 1984 | Eric Cunningham | Liberal | Ann Sloat | Progressive Conservative | Resignation to run federally. | No |
| Prescott and Russell | December 13, 1984 | Don Boudria | Liberal | Jean Poirier | Liberal | Resignation to run federally. | Yes |
| Ottawa East | December 13, 1984 | Albert J. Roy | Liberal | Bernard Grandmaître | Liberal | Resignation to run federally. | Yes |
| Ottawa Centre | December 13, 1984 | Michael Cassidy | New Democratic | Evelyn Gigantes | New Democratic | Resignation to run federally. | Yes |
| Hamilton Centre | December 13, 1984 | Sheila Copps | Liberal | Mike Davison | New Democratic | Resignation to run federally. | No |
| Stormont—Dundas—Glengarry | December 15, 1983 | Osie Villeneuve | Progressive Conservative | Noble Villeneuve | Progressive Conservative | Death | Yes |
| York South | November 4, 1982 | Donald C. MacDonald | New Democratic | Bob Rae | New Democratic | Resignation to create vacancy for NDP leader Bob Rae. | Yes |
| Hamilton West | June 17, 1982 | Stuart Smith | Liberal | Richard Allen | New Democratic | Resignation from legislature after his successor as Liberal leader was chosen. | No |

## 31st Legislative Assembly of Ontario 1977–1981

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Carleton | November 20, 1980 | Sid Handleman | Progressive Conservative | Robert C. Mitchell | Progressive Conservative | Resignation | Yes |
| Scarborough West | April 5, 1979 | Stephen Lewis | New Democratic | Richard Johnston | New Democratic | Resignation several months after his successor as Ontario NDP leader was chosen. | Yes |
| Wentworth | April 5, 1979 | Ian Deans | New Democratic | Colin Isaacs | New Democratic | Resignation after being defeated in his candidacy to lead the Ontario NDP. | Yes |
| Sault Ste. Marie | December 14, 1978 | John Rhodes | Progressive Conservative | Russ Ramsay | Progressive Conservative | Death. | Yes |
| Chatham—Kent | October 19, 1978 | Darcy McKeough | Progressive Conservative | Andrew Naismith Watson | Progressive Conservative | Resignation. | Yes |

## 30th Legislative Assembly of Ontario 1975–1977

no by-elections

## 29th Legislative Assembly of Ontario 1971–1975

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Carleton East | November 7, 1974 | Bert Lawrence | Progressive Conservative | Paul Frederick Taylor | Liberal | Resignation. | No |
| Stormont | October 17, 1974 | Fernand Guindon | Progressive Conservative | George Samis | New Democratic | Resignation to run federally. | No |
| Huron | March 15, 1973 | Charles MacNaughton | Progressive Conservative | Jack Riddell | Liberal | Resignation. | No |
| St. George | March 15, 1973 | Allan Lawrence | Progressive Conservative | Margaret Campbell | Liberal | Resignation to enter federal politics. | No |

## 28th Legislative Assembly of Ontario 1967–1971

| By-election | Date | Incumbent | Party | Party | Winner | Party | Party | Cause | Retained |
| Middlesex South | September 18, 1969 | Neil Leverne Olde | | Progressive Conservative | Kenneth Charles Bolton | | New Democratic | Death. | No |

## 27th Legislative Assembly of Ontario 1963–1967

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Kenora | September 22, 1966 | Robert Wayne Gibson | Liberal-Labour | Leo Bernier | Progressive Conservative | Death | No |
| Nipissing | September 15, 1965 | Leo Troy | Liberal | Richard Smith | Liberal | Death | Yes |
| Bracondale | September 15, 1965 | Joseph M. Gould | Liberal | George Ben | Liberal | Death | Yes |
| Riverdale | September 10, 1964 | Robert Macaulay | Progressive Conservative | Jim Renwick | New Democratic | Resigned to return to private life | No |
| Windsor—Sandwich | September 10, 1964 | Maurice Belanger | Liberal | Ivan Thrasher | Progressive Conservative | Death | No |

## 26th Legislative Assembly of Ontario 1959–1963

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Huron—Bruce | October 4, 1962 | John William Hanna | Progressive Conservative | Murray Gaunt | Liberal | Death | No |
| Beaches | January 18, 1962 | William Henry Collings | Progressive Conservative | Robert John Harris | Progressive Conservative | Death | Yes |
| Brant | January 18, 1962 | Harry Nixon | Liberal | Robert Nixon | Liberal | Death | Yes |
| Eglinton | January 18, 1962 | William James Dunlop | Progressive Conservative | Leonard Mackenzie Reilly | Progressive Conservative | Death | Yes |
| Kenora | January 18, 1962 | Albert Wren | Liberal-Labour | Robert Wayne Gibson | Liberal | Death | Yes |
| Renfrew South | January 18, 1962 | James Anthony Maloney | Progressive Conservative | Leonard Joseph Quilty | Liberal | Death | No |
| Simcoe Centre | September 29, 1960 | George Graham Johnston | Progressive Conservative | David Arthur Evans | Progressive Conservative | Death | Yes |
| Timiskaming | September 29, 1960 | Alexander Robert Herbert | Progressive Conservative | Phillip Hoffman | Progressive Conservative | Death | Yes |

## 25th Legislative Assembly of Ontario 1955–1959

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Hastings East | August 28, 1958† | Roscoe Robson | Progressive Conservative | Lloyd Harrison Price | Progressive Conservative | Appointed Sheriff | Yes |
| Lanark | August 28, 1958† | John Arthur McCue | Progressive Conservative | George Gomme | Progressive Conservative | Death | Yes |
| Cochrane North | May 12, 1958 | Philip Timothy Kelly | Progressive Conservative | René Brunelle | Progressive Conservative | Resignation | Yes |
| Huron | May 12, 1958 | Thomas Pryde | Progressive Conservative | Charles MacNaughton | Progressive Conservative | Death | Yes |
| Renfrew North | May 12, 1958 | Stanley Joseph Hunt | Progressive Conservative | Maurice Hamilton | Progressive Conservative | Resigned to enter federal politics | Yes |
| St. George | May 12, 1958 | Dana Porter | Progressive Conservative | Allan Lawrence | Progressive Conservative | Appointed Chief Justice of the Ontario Court of Appeal | Yes |
| Elgin | January 30, 1958 | Fletcher Stewart Thomas | Progressive Conservative | Ron McNeil | Progressive Conservative | Death | Yes |
| Lanark | October 24, 1957 | George Doucett | Progressive Conservative | John Arthur McCue | Progressive Conservative | Resigned to enter federal politics | Yes |
| Glengarry | September 5, 1957 | Osie Villeneuve | Progressive Conservative | Fernand Guindon | Progressive Conservative | Resigned to enter federal politics | Yes |
| Middlesex North | September 5, 1957 | Thomas L. Patrick | Progressive Conservative | William Atcheson Stewart | Progressive Conservative | Death | Yes |
| York West | October 18, 1956 | W. Elmer Brandon | Progressive Conservative | Leslie Rowntree | Progressive Conservative | Death | Yes |
| Renfrew South | January 12, 1956 | James Shannon Dempsey | Progressive Conservative | James Anthony Maloney | Progressive Conservative | Death | Yes |
† Won by acclamation

## 24th Legislative Assembly of Ontario 1951–1955

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Leeds | September 16, 1954 | Charles Gordon MacOdrum | Progressive Conservative | James Auld | Progressive Conservative | Death | Yes |
| Nipissing | September 16, 1954 | William Bruce Harvey | Progressive Conservative | Jean Marc Chaput | Progressive Conservative | Death | Yes |
| Russell | September 16, 1954 | Joseph Daniel Nault | Progressive Conservative | Gordon Lavergne | Progressive Conservative | Death | Yes |
| Simcoe East | February 8, 1954 | John Duncan McPhee | Progressive Conservative | Lloyd Averall Letherby | Progressive Conservative | Death | Yes |
| Niagara Falls | October 26, 1953 | William Houck | Liberal | Arthur Connaught Jolley | Progressive Conservative | Resigned to enter federal politics | No |

## 23rd Legislative Assembly of Ontario 1948–1951

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Leeds | October 31, 1949 | Walter Bain Reynolds | Progressive Conservative | Hugh Alexander Reynolds | Progressive Conservative | Death | Yes |
| Cochrane North | June 8, 1949 | John Carrère | Progressive Conservative | Marcel Léger | Progressive Conservative | Death | Yes |
| Parry Sound | December 9, 1948 | Charles Wilson Cragg | Progressive Conservative | Allister Johnston | Progressive Conservative | Death | Yes |

## 22nd Legislative Assembly of Ontario 1945–1948

| By-election | Date | Incumbent | Party | Party | Winner | Party | Party | Cause | Retained |
| Huron | February 16, 1948 | Robert Hobbs Taylor | | Progressive Conservative | Thomas Pryde | | Progressive Conservative | Death | Yes |

## 21st Legislative Assembly of Ontario 1943–1945

| By-election | Date | Incumbent | Party | Party | Winner | Party | Party | Cause | Retained |
| Haldimand—Norfolk | March 20, 1944 | Wallace William Walsh | | Progressive Conservative | Charles Hammond Martin | | Progressive Conservative | Death | Yes |

## 20th Legislative Assembly of Ontario 1937–1943

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Grey South | February 24, 1941† | Farquhar Oliver | United Farmers of Ontario | Farquhar Oliver | Liberal | Sought re-election upon appointment as Minister of Public Works | No |
| Ottawa East | November 27, 1940 | Paul Leduc | Liberal | Robert Laurier | Liberal | Resignation | Yes |
| Simcoe Centre | October 23, 1940† | Leonard Jennett Simpson | Liberal | Duncan McArthur | Liberal | Death | Yes |
| Simcoe East | February 14, 1939† | William Finlayson | Conservative | George A. Drew | Conservative | Resignation to provide a seat for Conservative leader Drew | Yes |
| Parkdale | October 5, 1938 | Fred McBrien | Conservative | William James Stewart | Conservative | Death | Yes |
| Waterloo South | September 28, 1938† | Norman Hipel | Liberal | Norman Hipel | Liberal | Sought re-election upon appointment as Minister of Labour | Yes |
| Brantford | July 20, 1938 | Morrison Mann MacBride | Independent-Liberal* | Louis Hagey | Liberal | Death | Yes |
| Lambton East | March 22, 1938 | Milton Duncan McVicar | Liberal | Charles Oliver Fairbank | Liberal | Death | Yes |
| Hamilton Centre | March 2, 1938 | William Frederick Schwenger | Liberal | John Newlands | Liberal | Resigned to become a judge | Yes |
| Sault Ste. Marie | November 23, 1937† | Richard McMeekin | Liberal | Colin Campbell | Liberal | Resignation to provide a seat for Campbell | Yes |
† 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

## 19th Legislative Assembly of Ontario 1934–1937

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Hastings East | December 9, 1936 | James Ferguson Hill | Conservative | Harold Edward Welsh | Conservative | Death | Yes |
| Nipissing | March 4, 1935 | Théodore Legault | Liberal | Joseph Marceau | Liberal | Death | Yes |
| Grey North | August 20, 1934 | David James Taylor | Liberal-Progressive | Roland Patterson | Liberal-Progressive | Resigned to accept appointment as Deputy Minister of Game and Fisheries | Yes |
| Wellington South | August 20, 1934 | Duncan Paul Munro | Liberal | James Harold King | Liberal | Death | Yes |
| Kenora | August 7, 1934† | Earl Hutchinson | Labour | Peter Heenan | Liberal | Resigned to become vice-chairman of Workmen's Compensation Board | No |
† Won by acclamation

## 18th Legislative Assembly of Ontario 1929–1934

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Kent East | January 3, 1934† | Philip James Henry | Conservative | Douglas Munro Campbell | Liberal | Death | No |
| York West | May 28, 1932 | Forbes Godfrey | Conservative | Henry Isaac Price | Conservative | Death | Yes |
| Wellington South | November 18, 1931 | Lincoln Goldie | Conservative | Duncan Paul Munro | Liberal | Died | No |
| Dundas | August 29, 1931† | George Holmes Challies | Conservative | George Holmes Challies | Conservative | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Norfolk | July 8, 1931 | John Strickler Martin | Conservative | Arthur Campbell Burt | Conservative | Death | Yes |
| Grenville | February 11, 1931 | Howard Ferguson | Conservative | James Alfred Sanderson | Conservative | Resigned to accept appointment as Canadian High Commissioner to the United Kingdom | Yes |
| Hamilton West | February 11, 1931 | Frederick Thomas Smye | Conservative | D'Arcy Argue Counsell Martin | Conservative | Death | Yes |
| Lanark South | October 29, 1930 | James Alexander Anderson | Conservative | Egerton Reuben Stedman | Conservative | Death | Yes |
| Nipissing | October 29, 1930 | Henri Morel | Conservative | Charles Robert Harrison | Conservative | Resigned to run in the 1930 federal election | Yes |
| Perth South | October 29, 1930 | David Bonis | Conservative | Charles Edward Richardson | Conservative | Death | Yes |
| Waterloo South | October 29, 1930 | Karl Kenneth Homuth | Conservative | Norman Hipel | Liberal | Resigned to run in the 1930 federal election | No |
| Algoma | October 18, 1930† | John Morrow Robb | Conservative | John Morrow Robb | Conservative | Sought re-election upon appointment as Minister of Health | Yes |
| Brantford | October 18, 1930† | William George Martin | Conservative | William George Martin | Conservative | Sought re-election upon appointment as Minister of Public Welfare | Yes |
| Peel | October 18, 1930† | Thomas Laird Kennedy | Conservative | Thomas Laird Kennedy | Conservative | Sought re-election upon appointment as Minister of Agriculture | Yes |
| Renfrew North | October 18, 1930† | Edward Arunah Dunlop | Conservative | Edward Arunah Dunlop | Conservative | Sought re-election upon appointment as Provincial Treasurer | Yes |
| York South | October 18, 1930† | Leopold Macaulay | Conservative | Leopold Macaulay | Conservative | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
† Won by acclamation

## 17th Legislative Assembly of Ontario 1926–1929

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Renfrew North | June 27, 1928 | Alexander Stuart | Conservative | Edward Arunah Dunlop | Conservative | Death | Yes |
| Bruce South | June 27, 1928 | Malcolm Alex McCallum | Progressive | Foster Graham Moffatt | Conservative | Election declared void | No |
| Hamilton East | June 27, 1928 | Leeming Carr | Conservative | William Robert Morrison | Conservative | Resigned to accept appointment as Sheriff of Wellington County | Yes |
| Prince Edward | November 1, 1927† | William Raney | United Farmers of Ontario | Horace Stanley Colliver | Conservative | Appointed to Supreme Court of Ontario | No |
† Won by acclamation

## 16th Legislative Assembly of Ontario 1923–1926

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Toronto Northwest A | July 7, 1924 | Thomas Crawford | Conservative | William Henry Edwards | Conservative | Resigned to accept appointment as Registrar | Yes |
| Waterloo South | June 23, 1924 | Karl Kenneth Homuth | Labour | Karl Kenneth Homuth | Labour | Election declared void | Yes |
| Lennox | October 22, 1923 | John Perry Vrooman | Liberal | Charles Wesley Hambly | Conservative | Death | No |
| York West | August 16, 1923† | Forbes Godfrey | Conservative | Forbes Godfrey | Conservative | Sought re-election upon appointment as Minister of Labour | Yes |
| York East | August 16, 1923† | George Stewart Henry | Conservative | George Stewart Henry | Conservative | Sought re-election upon appointment as Minister of Public Works and Highways | Yes |
| Wellington South | August 16, 1923† | Lincoln Goldie | Conservative | Lincoln Goldie | Conservative | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Sudbury | August 16, 1923† | Charles McCrea | Conservative | Charles McCrea | Conservative | Sought re-election upon appointment as Minister of Mines | Yes |
| Sault Ste. Marie | August 16, 1923† | James Winfield Lyons | Conservative | James Winfield Lyons | Conservative | Sought re-election upon appointment as Minister of Lands and Forests | Yes |
| Parkdale | August 16, 1923† | William Herbert Price | Conservative | William Herbert Price | Conservative | Sought re-election upon appointment as Provincial Treasurer | Yes |
| Norfolk South | August 16, 1923† | John Strickler Martin | Conservative | John Strickler Martin | Conservative | Sought re-election upon appointment as Minister of Agriculture | Yes |
| Kingston | August 16, 1923† | William Folger Nickle | Conservative | William Folger Nickle | Conservative | Sought re-election upon appointment as Attorney-General | Yes |
| Grenville | August 16, 1923† | George Howard Ferguson | Conservative | George Howard Ferguson | Conservative | Sought re-election upon appointment as Premier and Minister of Education | Yes |
† Won by acclamation

## 15th Legislative Assembly of Ontario 1919–1923

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Russell | October 23, 1922 | Damase Racine | Liberal | Alfred Goulet | Liberal | Death | Yes |
| Toronto Southeast A | October 23, 1922 | John O'Neill | Liberal | John Allister Currie | Conservative | Death | No |
| Kingston | February 6, 1922 | Arthur Edward Ross | Conservative | William Folger Nickle | Conservative | Resigned to run in the 1921 federal election | Yes |
| Oxford North | December 19, 1921 | John Alexander Calder | Liberal | David Munroe Ross | United Farmers of Ontario | Death | No |
| Toronto Northeast A | November 8, 1920 | Henry John Cody | Conservative | Alexander Cameron Lewis | Conservative | Resignation | Yes |
| Fort William | July 19, 1920† | Harry Mills | Labour | Harry Mills | Labour | Sought re-election upon appointment as Minister of Mines | Yes |
| Wellington East | February 23, 1920† | Albert Hellyer | United Farmers of Ontario | William Raney | United Farmers of Ontario | Resignation to provide a seat for Raney | Yes |
| Halton | February 16, 1920 | John Featherstone Ford | United Farmers of Ontario | Ernest Charles Drury | United Farmers of Ontario | Resignation to provide a seat for Drury | Yes |
| Kent East | February 9, 1920† | James B. Clark | United Farmers of Ontario | Manning Doherty | United Farmers of Ontario | Resignation to provide a seat for Doherty | Yes |
| Brant North | December 15, 1919† | Harry Nixon | United Farmers of Ontario | Harry Nixon | United Farmers of Ontario | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Wentworth North | December 15, 1919† | Frank Campbell Biggs | United Farmers of Ontario | Frank Campbell Biggs | United Farmers of Ontario | Sought re-election upon appointment as Minister of Public Works and Highways | Yes |
| Perth South | December 15, 1919† | Peter Smith | United Farmers of Ontario | Peter Smith | United Farmers of Ontario | Sought re-election upon appointment as Provincial Treasurer | Yes |
| Manitoulin | December 15, 1919† | Beniah Bowman | United Farmers of Ontario | Beniah Bowman | United Farmers of Ontario | Sought re-election upon appointment as Minister of Lands, Forests and Mines | Yes |
| Hamilton West | December 15, 1919† | Walter Rollo | Labour | Walter Rollo | Labour | Sought re-election upon appointment as Minister of Labour | Yes |
| Carleton | December 15, 1919† | Robert Henry Grant | United Farmers of Ontario | Robert Henry Grant | United Farmers of Ontario | Sought re-election upon appointment as Minister of Education | Yes |
† Won by acclamation

## 14th Legislative Assembly of Ontario 1914–1919

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Ontario North | February 18, 1919 | William Hoyle | Conservative | John Wesley Widdifield | United Farmers of Ontario | Death | No |
| St. Catharines | February 15, 1919 | Elisha Jessop | Conservative | Frederick Raymond Parnell | Conservative | Death | Yes |
| Huron North | December 2, 1918 | Armstrong Musgrove | Conservative | William Henry Fraser | Liberal | Resignation upon appointment as Postmaster of Wingham | No |
| Manitoulin | October 24, 1918 | Robert Roswell Gamey | Conservative | Beniah Bowman | United Farmers of Ontario | Death | No |
| Oxford North | September 23, 1918† | Newton Wesley Rowell | Liberal | John Alexander Calder | Liberal | Resigned to run in the 1917 federal election. | Yes |
| Lennox | August 29, 1918† | Thomas George Carscallen | Conservative | Reginald Amherst Fowler | Conservative | Death | Yes |
| York East | August 19, 1918 | George Stewart Henry | Conservative | George Stewart Henry | Conservative | Sought re-election upon appointment as Minister of Agriculture | | Yes |
| Toronto Northeast A | August 19, 1918 | Robert Allan Pyne | Conservative | Henry John Cody | Conservative | Resigned to accept position as Clerk of York County. | Yes |
| Toronto Northwest B | January 22, 1917 | William David McPherson | Conservative | William David McPherson | Conservative | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Simcoe West | January 15, 1917† | James Stoddart Duff | Conservative | William Torrance Allen | Conservative | Death | Yes |
| Toronto Southwest A | August 21, 1916 | James Joseph Foy | Conservative | Hartley Dewart | Liberal | Death | No |
| Perth North | July 10, 1916 | James Torrance | Conservative | Wellington Hay | Liberal | Appointed Registrar | No |
| Muskoka | June 12, 1916† | Samuel Henry Armstrong | Conservative | George Walter Ecclestone | Conservative | Death | Yes |
| Peel | February 24, 1916 | James Robinson Fallis | Conservative | William James Lowe | Liberal | Resignation | No |
| Algoma | October 25, 1915† | Albert Grigg | Conservative | John Morrow Robb | Conservative | Resignation upon appointment as Deputy Minister of Crown Lands | Yes |
| Grenville | January 7, 1915† | George Howard Ferguson | Conservative | George Howard Ferguson | Conservative | Sought re-election upon appointment as Minister of Lands, Forests and Mines | Yes |
| Renfrew South | January 7, 1915† | Thomas William McGarry | Conservative | Thomas William McGarry | Conservative | Sought re-election upon appointment as Provincial Treasurer | Yes |
| Dundas | December 7, 1914 | Sir James Whitney | Conservative | Irwin Foster Hilliard | Conservative | Death | Yes |
| Hamilton West | November 18, 1914 | John Strathearn Hendrie | Conservative | John Allan | Conservative | Appointed Lieutenant Governor of Ontario | Yes |
| Elgin West | October 21, 1914† | Findlay George MacDiarmid | Conservative | Findlay George MacDiarmid | Conservative | Sought re-election upon appointment as Minister of Public Works | Yes |
† Won by acclamation

## 13th Legislative Assembly of Ontario 1911–1914

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Middlesex East | November 27, 1913 | George Wesley Neely | Conservative | John McFarlan | Conservative | Death | Yes |
| Peel | November 3, 1913 | Samuel Charters | Conservative | James Robinson Fallis | Conservative | Appointed Registrar | Yes |
| York East | September 8, 1913 | Alexander McCowan | Conservative | George Stewart Henry | Conservative | Appointed Sheriff of York County | Yes |
| Grey North | July 14, 1913 | Alexander Grant MacKay | Liberal | Colin Stewart Cameron | Conservative | Resignation upon entering provincial politics in Alberta | No |
| Grey Centre | June 2, 1913† | Isaac Benson Lucas | Conservative | Isaac Benson Lucas | Conservative | Sought re-election upon appointment as Provincial Treasurer | Yes |
| Lanark South | March 19, 1913 | Arthur Matheson | Conservative | John Charles Ebbs | Conservative | Death | Yes |
| Muskoka | November 5, 1912† | Arthur Arnold Mahaffy | Conservative | Samuel Henry Armstrong | Conservative | Appointed a Judge | Yes |
| Waterloo North | October 28, 1912 | Henry George Lackner | Conservative | Charles Henry Mills | Conservative | Appointed Sheriff of Waterloo County | Yes |
| Middlesex East | October 28, 1912 | Robert Sutherland | Liberal | George Wesley Neely | Conservative | Death | No |
† Won by acclamation

## 12th Legislative Assembly of Ontario 1908–1911

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Wellington South | October 21, 1910† | Joseph Patrick Downey | Conservative | John Ransom Howitt | Conservative | Appointed Superintendent for the Ontario Asylum for Idiots | Yes |
| Middlesex North | December 6, 1909 | Duncan Campbell Ross | Liberal | James William Doyle | Conservative | Resignation to enter federal politics | No |
| Victoria East | May 25, 1909 | John Hilliard Carnegie | Conservative | Robert Mercer Mason | Conservative | Resignation upon appointment as Distributor of Law Stamps | Yes |
| Algoma | December 17, 1908† | William Ross Smyth | Conservative | Albert Grigg | Conservative | Resignation to enter federal politics | Yes |
| Simcoe West | October 23, 1908† | James Stoddart Duff | Conservative | James Stoddart Duff | Conservative | Sought re-election upon appointment as Minister of Agriculture | Yes |
† Won by acclamation

## 11th Legislative Assembly of Ontario 1905–1908

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Brockville | October 7, 1907 | George Perry Graham | Liberal | Albert Edward Donovan | Conservative | Resignation on entering federal politics | No |
| Dufferin | July 24, 1907 | Frederick William Lewis | Conservative | Charles Robert McKeown | Conservative | Death | Yes |
| York West | June 1, 1907 | Joseph Wesley St. John | Conservative | Forbes Godfrey | Conservative | Death | Yes |
| Carleton | March 18, 1907 | George Nelson Kidd | Conservative | Robert McElroy | Conservative | Death | Yes |
| Middlesex West | February 20, 1907 | George William Ross | Liberal | Duncan Campbell Ross | Liberal | Appointed to the Senate | Yes |
| Hamilton East | December 4, 1906 | Henry Carscallen | Conservative | Allan Studholme | Labour | Death | No |
| Cardwell | September 21, 1906† | Edward Alfred Little | Conservative | Alexander Ferguson | Conservative | Appointed Registrar | Yes |
| Toronto North | February 22, 1906 | William Beattie Nesbitt | Conservative | William Kirkpatrick McNaught | Conservative | Appointed registrar of West Toronto | Yes |
| Kingston | January 29, 1906 | Edward John Barker Pense | Liberal | Edward John Barker Pense | Liberal | Election declared void | Yes |
| Nipissing East | June 13, 1905† | Charles Lamarche | Conservative | Francis Cochrane | Conservative | Resignation to provide a seat for Cochrane | Yes |
| Toronto South | February 21, 1905† | James Joseph Foy | Conservative | James Joseph Foy | Conservative | Sought re-election upon appointment as Commissioner of Crown Lands | Yes |
| Toronto East | February 21, 1905† | Robert Allan Pyne | Conservative | Robert Allan Pyne | Conservative | Sought re-election upon appointment as Minister of Education | Yes |
| Perth South | February 21, 1905† | Samuel Nelson Monteith | Conservative | Samuel Nelson Monteith | Conservative | Sought re-election upon appointment as Minister of Agriculture | Yes |
| Lanark South | February 21, 1905† | Arthur James Matheson | Conservative | Arthur James Matheson | Conservative | Sought re-election upon appointment as Provincial Treasurer | Yes |
| Lambton West | February 21, 1905† | William John Hanna | Conservative | William John Hanna | Conservative | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Essex North | February 21, 1905† | Joseph Octave Reaume | Conservative | Joseph Octave Reaume | Conservative | Sought re-election upon appointment as Commissioner of Public Works | Yes |
| Dundas | February 21, 1905† | James Pliny Whitney | Conservative | James Pliny Whitney | Conservative | Sought re-election upon appointment as Premier and Attorney-General | Yes |
† Won by acclamation

## 10th Legislative Assembly of Ontario 1902–1904

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Oxford North | January 26, 1904 | Andrew Pattulo | Liberal | James S. Munro | Liberal | Death | Yes |
| Renfrew North | December 26, 1903 | John W. Munro | Liberal | Edward Arunah Dunlop | Conservative | Death | No |
| Sault Ste. Marie | October 27, 1903 | Andrew Miscampbell | Conservative | Charles Napier Smith | Liberal | Void Election | No |
| Muskoka | October 27, 1903 | Samuel Bridgeland | Liberal | Arthur Arnold Mahaffy | Conservative | Death | No |
| York North | February 26, 1903 | Elihu James Davis | Liberal | Elihu James Davis | Liberal | Resignation in exchange for withdrawal of election petition | Yes |
| Bruce Centre | February 26, 1903 | Hugh Clark | Conservative | Hugh Clark | Conservative | Void Election | Yes |
| Perth North | January 7, 1903 | John C. Monteith | Conservative | John Brown | Liberal | Void Election | No |
| Norfolk North | January 7, 1903 | Frederick Snider | Conservative | Archibald Little | Liberal | Void Election | No |
| Grey North | January 7, 1903 | Alexander Grant MacKay | Liberal | Alexander Grant MacKay | Liberal | Void Election | Yes |

## 9th Legislative Assembly of Ontario 1898–1902

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Kingston | January 30, 1902† | William Harty | Liberal | Edward John Barker Pense | Liberal | Resignation to enter federal politics | Yes |
| Huron West | December 4, 1901 | James Thompson Garrow | Liberal | James Thompson Garrow | Liberal | Void Election | Yes |
| Kent East | November 4, 1901† | Robert Ferguson | Liberal | John Lee | Liberal | Death | Yes |
| London | July 9, 1901 | Francis Baxter Leys | Liberal | Francis Baxter Leys | Liberal | Sought re-election in support of removing a dam on the Thames River | Yes |
| Welland | December 13, 1900 | William Manley German | Liberal | John Franklin Gross | Liberal | Resignation to enter federal politics | Yes |
| Waterloo North | October 31, 1900† | Louis Jacob Breithaupt | Liberal | Louis Jacob Breithaupt | Liberal | Void Election | Yes |
| Renfrew North | June 19, 1900† | Andrew Thomas White | Conservative | John W. Munro | Liberal | Death | No |
| Middlesex East | January 31, 1900 | Thomas D. Hodgins | Conservative | Thomas Robson | Conservative | Death | Yes |
| Brant South | December 12, 1899 | Arthur Sturgis Hardy | Liberal | Thomas Hiram Preston | Liberal | Resignation | Yes |
| Elgin East | December 12, 1899 | Charles Andrew Brower | Conservative | Charles Andrew Brower | Conservative | Void Election | Yes |
| Elgin West | December 12, 1899 | Donald Macnish | Liberal | Findlay George MacDiarmid | Conservative | Void Election | No |
| Ontario South | December 12, 1899 | John Dryden | Liberal | John Dryden | Liberal | Void Election | Yes |
| Renfrew South | November 14, 1899 | Robert Adam Campbell | Liberal | Francis Robert Latchford | Liberal | Resignation to provide a seat for Latchford | Yes |
| Peterborough West | November 7, 1899† | James Robert Stratton | Liberal | James Robert Stratton | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Waterloo North | May 23, 1899 | Henry George Lackner | Conservative | Louis Jacob Breithaupt | Liberal | Void Election | No |
| Perth South | February 28, 1899 | William Caven Moscrip | Liberal | Samuel Nelson Monteith | Conservative | Void Election | No |
| Elgin West | January 12, 1899 | Findlay George MacDiarmid | Conservative | Donald Macnish | Liberal | Void Election | No |
| Hastings North | December 27, 1898 | William John Allen | Conservative | William John Allen | Conservative | Resignation in exchange for withdrawal of election petition | Yes |
| Nipissing | December 27, 1898 | John Loughrin | Liberal | John Loughrin | Liberal | Void Election | Yes |
| Northumberland East | December 14, 1898 | John Henry Douglas | Liberal | John Henry Douglas | Liberal | Void Election | Yes |
| Halton | December 8, 1898 | John Roaf Barber | Liberal | John Roaf Barber | Liberal | Void Election | Yes |
| Huron West | December 8, 1898 | James Thompson Garrow | Liberal | James Thompson Garrow | Liberal | Void Election | Yes |
| Lennox | November 18, 1898 | Bowen Ebenezer Aylsworth | Liberal | Bowen Ebenezer Aylsworth | Liberal | Void Election | Yes |
| Ontario South | November 1, 1898 | Charles Calder | Conservative | John Dryden | Liberal | Void Election | No |
| Wellington East | October 27, 1898 | John Craig | Liberal | John Morison Gibson | Liberal | Death | Yes |
† Won by acclamation

## 8th Legislative Assembly of Ontario 1894–1898

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Essex South | October 20, 1896 | William Douglas Balfour | Liberal | John Allan Auld | Liberal | Death | Yes |
| York North | September 8, 1896† | Elihu James Davis | Liberal | Elihu James Davis | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Oxford North | September 7, 1896 | Oliver Mowat | Liberal | Andrew Pattulo | Liberal | Appointed to the Senate | Yes |
| Essex South | August 4, 1896† | William Douglas Balfour | Liberal | William Douglas Balfour | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Wentworth South | January 24, 1896 | Nicholas Awrey | Liberal | John Dickenson | Liberal | Appointed Sheriff of Wentworth County | Yes |
| Wellington West | January 24, 1896 | George Tucker | Conservative-PPA | James Tucker | Conservative | Void Election | Yes |
| Kingston | October 8, 1895† | William Harty | Liberal | William Harty | Liberal | Void Election | Yes |
| Brant North | May 20, 1895† | William Bruce Wood | Liberal | Daniel Burt | Liberal | Resignation | Yes |
| Haldimand | March 19, 1895 | John Senn | Conservative | Jacob Baxter | Liberal | Void Election | No |
| Algoma West | January 29, 1895 | James M. Savage | Conservative | James Conmee | Liberal | Void Election | No |
| Kingston | January 28, 1895 | Edward H. Smythe | Conservative | William Harty | Liberal | Void Election | No |
| London | November 20, 1894 | William Ralph Meredith | Conservative | Thomas Saunders Hobbs | Liberal | Appointed a judge | No |
† Won by acclamation

## 7th Legislative Assembly of Ontario 1890–1894

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Lanark South | February 16, 1894 | Nathaniel McLenaghan | Conservative | James Maitland Clarke | Liberal | Resignation | No |
| Lambton East | December 2, 1893 | Hugh McKenzie | Liberal | Peter Duncan McCallum | Independent Conservative | Death | No |
| Bruce North | December 2, 1893 | David Porter | Liberal | Daniel McNaughton | Liberal | Death | Yes |
| Toronto | February 28, 1893 | Nelson Gordon Bigelow | Liberal | George Ryerson | Conservative | Death | No |
| Peel | December 30, 1892 | Kenneth Chisholm | Liberal | John Smith | Liberal | Appointed Registrar for Peel County | Yes |
| Toronto | April 29, 1892 | Henry Edward Clarke | Conservative | Nelson Gordon Bigelow | Liberal | Death | No |
| Renfrew North | February 29, 1892 | Arunah Dunlop | Conservative | Henry Barr | Liberal | Death | No |
| Kingston | February 29, 1892 | James Henry Metcalfe | Conservative | William Harty | Liberal | Resignation to enter federal politics | No |
| Wellington East | November 10, 1891 | Charles Clarke | Liberal | James Kirkwood | Liberal | Appointed Clerk of the House | Yes |
| Grey South | April 2, 1891† | James Hill Hunter | Liberal | Gilbert McKechnie | Liberal | Death | Yes |
| Bruce North | March 3, 1891 | John George | Conservative | David Porter | Liberal | Void Election | No |
| Hamilton | February 24, 1891 | Thomas Henry Stinson | Conservative | John Morison Gibson | Liberal | Void Election | No |
| Perth North | January 23, 1891 | Alfred Emanuel Ahrens | Liberal | Thomas Magwood | Conservative | Void Election | No |
| Norfolk South | January 23, 1891 | William Andrew Charlton | Liberal | William Andrew Charlton | Liberal | Void Election | Yes |
| Norfolk North | January 23, 1891 | John Bailey Freeman | Liberal | Edwin Clarendon Carpenter | Liberal | Death | Yes |
| Durham East | January 23, 1891 | George Campbell | Conservative-Equal Rights | George Campbell | Conservative-Equal Rights | Void Election | Yes |
| Ontario South | September 30, 1890† | John Dryden | Liberal | John Dryden | Liberal | Sought re-election upon appointment as Commissioner of Agriculture | Yes |
| Monck | September 30, 1890† | Richard Harcourt | Liberal | Richard Harcourt | Liberal | Sought re-election upon appointment as Provincial Treasurer | Yes |
† Won by acclamation

## 6th Legislative Assembly of Ontario 1886–1890

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Lambton West | October 19, 1889† | Timothy Blair Pardee | Liberal | Charles MacKenzie | Liberal | Death | Yes |
| Hamilton | January 31, 1889† | John Morison Gibson | Liberal | John Morison Gibson | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Northumberland East | October 11, 1888 | Richard Clarke | Liberal | William Arnson Willoughby | Conservative | Death | No |
| Frontenac | October 11, 1888 | Henry Wilmot | Conservative | Hugh Smith | Conservative | Death | Yes |
| Elgin East | October 11, 1888 | Thomas McIntyre Nairn | Liberal | James Charles Dance | Liberal | Death | Yes |
| Lanark North | October 4, 1888† | Daniel Hilliard | Liberal | William Clyde Caldwell | Liberal | Death | Yes |
| York North | May 23, 1888† | Joseph Henry Widdifield | Liberal | Elihu James Davis | Liberal | Resignation | Yes |
| Simcoe East | May 16, 1888† | Charles Alfred Drury | Liberal | Charles Alfred Drury | Liberal | Sought re-election upon appointment as Commissioner of Agriculture | Yes |
| Northumberland East | February 1, 1888 | William Arnson Willoughby | Conservative | Richard Clarke | Liberal | Void Election | No |
| Dundas | January 31, 1888 | Theodore F. Chamberlain | Liberal | James Pliny Whitney | Conservative | Void Election | No |
† Won by acclamation

## 5th Legislative Assembly of Ontario 1883–1886

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Algoma East | June 29, 1885 | New Seat | | Robert Adam Lyon | Liberal | Algoma divided | N/A |
| Simcoe East | June 26, 1885 | Charles Alfred Drury | Liberal | Charles Alfred Drury | Liberal | Void Election | Yes |
| Lennox | June 26, 1885 | George Douglas Hawley | Liberal | George Douglas Hawley | Liberal | Void Election | Yes |
| Algoma West | June 26, 1885 | New Seat | | James Conmee | Liberal | Algoma divided | N/A |
| Kent East | June 19, 1885† | Daniel McCraney | Liberal | Robert Ferguson | Liberal | Death | Yes |
| Renfrew South | January 27, 1885 | John Francis Dowling | Liberal | John Francis Dowling | Liberal | Void Election | Yes |
| Lennox | August 28, 1884 | Alexander Hall Roe | Conservative | George Douglas Hawley | Liberal | Death | No |
| Muskoka and Parry Sound | July 23, 1884 | Frederick G. Fauquier | Conservative | Jacob William Dill | Liberal | Void Election | No |
| Grey East | March 18, 1884 | Abram William Lauder | Conservative | Neil McColman | Conservative | Death | Yes |
| Oxford South | March 5, 1884 | Adam Crooks | Liberal | George Atwell Cooke | Liberal | Crooks declared "incurably insane" and seat vacated | Yes |
| Renfrew South | January 18, 1884 | John Francis Dowling | Liberal | John Francis Dowling | Liberal | Void Election | Yes |
| Simcoe West | December 14, 1883 | Orson James Phelps | Liberal | Orson James Phelps | Liberal | Void Election | Yes |
| Middlesex West | December 14, 1883 | Alexander Johnston | Conservative | George William Ross | Liberal | Void Election | No |
| Cardwell | December 14, 1883 | William Henry Hammell | Conservative | William Henry Hammell | Conservative | Void Election | Yes |
| Huron West | November 16, 1883† | Alexander McLagan Ross | Liberal | Alexander McLagan Ross | Liberal | Sought re-election upon appointment as Provincial Treasurer and Commissioner of Agriculture | Yes |
| Brant North | June 16, 1883 | James Young | Liberal | James Young | Liberal | Sought re-election upon appointment as Provincial Treasurer and Commissioner of Agriculture | Yes |
† Won by acclamation

## 4th Legislative Assembly of Ontario 1879–1883

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Muskoka and Parry Sound | October 30, 1882 | John Classon Miller | Liberal | James Whitney Bettes | Liberal | Resignation to contest the 1882 federal election | Yes |
| Waterloo South | October 18, 1882 | James Livingston | Liberal | Isaac Master | Liberal | Resignation to contest the 1882 federal election | Yes |
| Simcoe East | October 18, 1882 | Herman Henry Cook | Liberal | Charles Alfred Drury | Liberal | Resignation to contest the 1882 federal election | Yes |
| Renfrew North | October 18, 1882† | Thomas Murray | Liberal | William Balmer McAllister | Conservative | Resignation to contest the 1882 federal election | Yes* |
| Hastings West | October 18, 1882 | Alexander Robertson | Conservative | Baltis Rose | Conservative | Resignation to contest the 1882 federal election | Yes |
| Glengarry | October 18, 1882 | Donald Macmaster | Conservative | James Rayside | Liberal | Resignation to contest the 1882 federal election | No |
| Essex South | October 18, 1882 | Lewis Wigle | Conservative | William Douglas Balfour | Liberal | Resignation to contest the 1882 federal election | No |
| Bruce South | October 18, 1882 | Rupert Mearse Wells | Liberal | Hamilton Parke O'Connor | Liberal | Resignation to contest the 1882 federal election | Yes |
| Peterborough West | August 24, 1881† | William Hepburn Scott | Conservative | Robert Kincaid | Conservative | Death | Yes |
| Durham East | June 29, 1881 | John Rosevear | Conservative | Charles Herbert Brereton | Conservative | Death | Yes |
| Waterloo North | June 27, 1881 | Moses Springer | Liberal | Elias Weber Bingeman Snider | Liberal | Resignation to become Sheriff of Waterloo County | Yes |
| Ontario North | June 4, 1881 | Thomas Paxton | Liberal | Frank Madill | Conservative | Resignation to become Sheriff of Ontario County | No |
| Prescott | April 14, 1881 | William Harkin | Conservative | Albert Hagar | Liberal | Death | No |
| Hastings West | January 30, 1880 | Alexander Robertson | Conservative | Alexander Robertson | Conservative | Void Election | Yes |
| Stormont | January 23, 1880 | Joseph Kerr | Conservative | Joseph Kerr | Conservative | Void Election | Yes |
| Dufferin | January 9, 1880 | John Barr | Conservative | William Jelly | Conservative | Void Election | Yes |
† Won by acclamation
*McAllister was a supporter of Mowat's government

## 3rd Legislative Assembly of Ontario 1875–1879

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Toronto East | December 21, 1878 | Matthew Crooks Cameron | Conservative | Alexander Morris | Conservative | Appointed a judge | Yes |
| Monck | December 21, 1878 | Henry Ryan Haney | Liberal | Richard Harcourt | Liberal | Death | Yes |
| Simcoe South | October 29, 1878 | William McDougall | Independent Liberal | William James Parkhill | Conservative | Resignation to contest the 1878 federal election | No |
| Essex North | October 29, 1878 | James Colebrooke Patterson | Conservative | Solomon White | Conservative | Resignation to contest the 1878 federal election | Yes |
| Elgin West | October 29, 1878 | Thomas Hodgins | Liberal | David McLaws | Liberal | Resignation to contest the 1878 federal election | Yes |
| Algoma | October 8, 1878† | Simon James Dawson | Liberal | Robert Adam Lyon | Liberal | Resignation to contest the 1878 federal election | Yes |
| Brant South | March 29, 1877† | Arthur Sturgis Hardy | Liberal | Arthur Sturgis Hardy | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Waterloo South | February 19, 1877 | John Fleming | Liberal | Isaac Master | Liberal | Death | Yes |
| Frontenac | February 12, 1877 | Peter Graham | Conservative | Delino Dexter Calvin | Conservative | Death | Yes |
| Wellington South | October 11, 1876† | Peter Gow | Liberal | James Massie | Liberal | Resignation to become Sheriff of Wellington County | Yes |
| Northumberland East | November 9, 1875 | James Marshall Ferris | Liberal | James Marshall Ferris | Liberal | Void Election | Yes |
| Halton | November 2, 1875 | William Barber | Liberal | William Durie Lyon | Liberal | Void Election | Yes |
| Grey North | October 30, 1875 | Thomas Scott | Conservative | David Creighton | Conservative | Void Election | Yes |
| Wentworth North | October 29, 1875 | Thomas Stock | Conservative | James McMahon | Liberal | Void Election | No |
| Peterborough West | October 26, 1875 | George Albertus Cox | Liberal | William Hepburn Scott | Conservative | Void Election | No |
| Victoria North | September 29, 1875 | John David Smith | Liberal | Duncan McRae | Conservative | Void Election | No |
| Wellington West | September 27, 1875 | John McGowan | Liberal-Conservative | John McGowan | Liberal-Conservative | Void Election | Yes |
| Dundas | September 25, 1875 | Andrew Broder | Conservative | Andrew Broder | Conservative | Void Election | Yes |
| Peterborough East | September 24, 1875 | John C. O'Sullivan | Conservative | John C. O'Sullivan | Conservative | Void Election | Yes |
| Kent East | September 17, 1875 | Archibald McKellar | Liberal | Daniel McCraney | Liberal | Appointed Sheriff of Wentworth County | Yes |
| Essex South | September 17, 1875 | Lewis Wigle | Conservative | Lewis Wigle | Conservative | Void Election | Yes |
| Oxford South | September 11, 1875 | Adam Oliver | Liberal | Adam Crooks | Liberal | Void Election | Yes |
| Russell | August 12, 1875 | Adam Jacob Baker | Conservative | Adam Jacob Baker | Conservative | Void Election | Yes |
| Victoria South | August 10, 1875 | Samuel Casey Wood | Liberal | Samuel Casey Wood | Liberal | Sought re-election upon appointment as Provincial Secretary and Commissioner of Agriculture | Yes |
| Cornwall | July 17, 1875 | Alexander Fraser McIntyre | Conservative | John Goodall Snetsinger | Liberal | Void Election | No |
| Welland | July 2, 1875 | James Currie | Liberal | James Currie | Liberal | Void Election | Yes |
| Monck | June 22, 1875 | Henry Ryan Haney | Liberal | Henry Ryan Haney | Liberal | Void Election | Yes |
| Ontario North | June 21, 1875 | Thomas Paxton | Liberal | Thomas Paxton | Liberal | Void Election | Yes |
| Simcoe South | May 26, 1875 | D'Arcy Boulton | Conservative | William McDougall | Independent Liberal | Death | No |
† Won by acclamation

## 2nd Legislative Assembly of Ontario 1871–1874

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Peterborough West | July 30, 1874 | Thomas McCulloch Fairbairn | Liberal | William Hepburn Scott | Conservative | Death | No |
| Wellington North | February 20, 1874 | Robert McKim | Liberal | John McGowan | Conservative | Resignation to enter federal politics | No |
| Perth North | February 14, 1874 | Andrew Monteith | Conservative | Thomas Mayne Daly | Conservative | Resignation to enter federal politics | Yes |
| Oxford South | January 19, 1874† | Adam Oliver | Liberal | Adam Oliver | Liberal | Resignation due to not being appointed Sheriff of Oxford County and selling timber to the provincial government | Yes |
| Ottawa | January 18, 1874 | Richard William Scott | Liberal | Daniel John O'Donoghue | Independent Labour | Appointed to the Senate | Yes |
| Simcoe South | December 30, 1873 | Thomas Roberts Ferguson | Conservative | D'Arcy Boulton | Conservative | Resignation | Yes |
| Peel | December 19, 1873 | John Coyne | Conservative | Kenneth Chisholm | Liberal | Death | No |
| Grenville South | December 9, 1873† | Christopher Finlay Fraser | Liberal | Christopher Finlay Fraser | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Leeds South | December 1873† | Herbert Stone MacDonald | Conservative | John Godkin Giles | Conservative | Resignation to be appointed to the county court | Yes |
| Huron South | October 16, 1873 | Robert Gibbons | Liberal | Archibald Bishop | Liberal | Resignation to become Sheriff of Huron County | Yes |
| Brant South | April 28, 1873 | Edmund Burke Wood | Conservative | Arthur Sturgis Hardy | Liberal | Resignation to enter federal politics | No |
| Oxford North | November 29, 1872† | George Perry | Liberal | Oliver Mowat | Liberal | Resignation to provide a seat for Mowat | Yes |
| Lambton | November 13, 1872† | Timothy Blair Pardee | Liberal | Timothy Blair Pardee | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Grenville South | October 16, 1872 | Christopher Finlay Fraser | Liberal | Christopher Finlay Fraser | Liberal | Void Election | Yes |
| Middlesex West | September 17, 1872 | Alexander Mackenzie | Liberal | John Watterworth | Liberal | Resignation upon abolition of the dual mandate | Yes |
| Bruce South | September 14, 1872 | Edward Blake | Liberal | Rupert Mearse Wells | Liberal | Resignation upon abolition of the dual mandate | Yes |
| Monck | September 1872 | Lachlin McCallum | Conservative | Henry Ryan Haney | Liberal | Resignation upon abolition of the dual mandate | No |
| London | August 26, 1872 | John Carling | Conservative | William Ralph Meredith | Conservative | Resignation upon abolition of the dual mandate | Yes |
| Lanark North | August 23, 1872 | Daniel Galbraith | Liberal | William Clyde Caldwell | Liberal | Resignation to enter federal politics | Yes |
| Cornwall | July 13, 1872 | John Sandfield Macdonald | Conservative | John Goodall Snetsinger | Liberal | Death | No |
| Grenville South | March 26, 1872 | Mcneil Clarke | Conservative | Christopher Finlay Fraser | Liberal | Death | No |
| Toronto West | January 9, 1872 | Adam Crooks | Liberal | Adam Crooks | Liberal | Sought re-election upon appointment as Attorney-General | Yes |
| Bothwell | January 6, 1872† | Archibald McKellar | Liberal | Archibald McKellar | Liberal | Sought re-election upon appointment as Commissioner of Agriculture and Public Works | Yes |
| Middlesex West | January 5, 1872† | Alexander Mackenzie | Liberal | Alexander Mackenzie | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Bruce South | January 5, 1872† | Edward Blake | Liberal | Edward Blake | Liberal | Resignation to re-contest upon being appointed Premier | Yes |
| Northumberland West | January 5, 1872 | Alexander Fraser | Liberal | Charles Gifford | Conservative | Resignation | No |
| Wellington South | January 4, 1872† | Peter Gow | Liberal | Peter Gow | Liberal | Sought re-election upon appointment as Provincial Secretary and Registrar | Yes |
| Ottawa | January 4, 1872† | Richard William Scott | Liberal | Richard William Scott | Liberal | Sought re-election upon appointment as Commissioner of Crown Lands | Yes |
| Stormont | January 3, 1872 | William Colquhoun | Conservative | James Bethune | Liberal | Void Election | No |
| Simcoe North | January 2, 1872 | William Davis Ardagh | Conservative | William Davis Ardagh | Conservative | Void Election | Yes |
| Carleton | January 2, 1872 | George William Monk | Conservative | George William Monk | Conservative | Void Election | Yes |
| Prince Edward | December 29, 1871 | Gideon Striker | Liberal | James Simeon McCuaig | Conservative | Void Election | No |
| Prince Edward | December 29, 1871 | James Simeon McCuaig | Conservative | Gideon Striker | Liberal | By-election result reversed August 29, 1872 | No |
| Grey South | December 29, 1871 | Abram William Lauder | Conservative | Abram William Lauder | Conservative | Void Election | Yes |
| Prescott | December 27, 1871† | George Wellesley Hamilton | Conservative | George Wellesley Hamilton | Conservative | Void Election | Yes |
| Durham West | December 27, 1871† | Edward Blake | Liberal | John McLeod | Liberal | Chose to sit for Bruce South | Yes |
† Won by acclamation

## 1st Legislative Assembly of Ontario 1867–1871

| By-election | Date | Incumbent | Party | Winner | Party | Cause | Retained |
| Prince Edward | June 29, 1870 | Absalom Greeley | Liberal | William Anderson | Conservative | Appointed Sheriff of Prince Edward County | No |
| Renfrew North | December 1, 1869 | John Supple | Conservative | Thomas Murray | Liberal | Resignation | No |
| Lanark South | February 3–4, 1869 | William McNairn Shaw | Conservative | Abraham Code | Conservative | Death | Yes |
| Frontenac | October 19, 1868 | Henry Smith | Conservative | Delino Dexter Calvin | Conservative | Death | Yes |
| Niagara | December 1867 | Donald Robertson | Conservative | Stephen Richards | Conservative | Appointed Coroner | Yes |