# List of New South Wales state by-elections

This is a list of by-elections for the New South Wales 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 independents and minor parties in grey; for the Free Trade Party in yellow and for the Protectionist Party in cyan.
Fifty-eighth Legislative Assembly 2023–2027 :
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Port Macquarie | Leslie Williams | | Liberal | Resigned | 15 March 2025 | | | |
| Pittwater | Rory Amon | | Liberal | Resigned | 19 October 2024 | Jacqui Scruby | | Independent |
| Epping | Dominic Perrottet | | Liberal | Resigned | 19 October 2024 | Monica Tudehope | | Liberal |
| Hornsby | Matt Kean | | Liberal | Resigned | 19 October 2024 | James Wallace | | Liberal |
| Northern Tablelands | Adam Marshall | | National | Resigned | 22 June 2024 | Brendan Moylan | | National |
| Fifty-seventh Legislative Assembly 2019–2023 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Bega | Andrew Constance | | Liberal | Resigned to contest federal seat of Gilmore | 12 February 2022 | Michael Holland | | Labor |
| Monaro | John Barilaro | | National | Resigned | 12 February 2022 | Nichole Overall | | National |
| Strathfield | Jodi McKay | | Labor | Resigned | 12 February 2022 | Jason Yat-Sen Li | | Labor |
| Willoughby | Gladys Berejiklian | | Liberal | Resigned due to ICAC investigation. | 12 February 2022 | Tim James | | Liberal |
| Upper Hunter | Michael Johnsen | | National | Resigned due to police investigation | 22 May 2021 | Dave Layzell | | National |
| Fifty-sixth Legislative Assembly 2015–2019 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Wagga Wagga | Daryl Maguire | | Liberal | Resigned due to ICAC investigation | 8 September 2018 | Joe McGirr | | Independent |
| Blacktown | John Robertson | | Labor | Resigned | 14 October 2017 | Stephen Bali | | Labor |
| Cootamundra | Katrina Hodgkinson | | National | Resigned | 14 October 2017 | Steph Cooke | | National |
| Murray | Adrian Piccoli | | National | Resigned | 14 October 2017 | Austin Evans | | National |
| Gosford | Kathy Smith | | Labor | Resigned due to ill health | 8 April 2017 | Liesl Tesch | | Labor |
| Manly | Mike Baird | | Liberal | Resigned | 8 April 2017 | James Griffin | | Liberal |
| North Shore | Jillian Skinner | | Liberal | Resigned | 8 April 2017 | Felicity Wilson | | Liberal |
| Canterbury | Linda Burney | | Labor | Resigned to contest federal seat of Barton | 12 November 2016 | Sophie Cotsis | | Labor |
| Orange | Andrew Gee | | National | Resigned to contest federal seat of Calare | 12 November 2016 | Philip Donato | | SFF |
| Wollongong | Noreen Hay | | Labor | Resigned | 12 November 2016 | Paul Scully | | Labor |
| Fifty-fifth Legislative Assembly 2011–2015 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Newcastle | Tim Owen | | Liberal | Resigned due to ICAC investigation | 25 October 2014 | Tim Crakanthorp | | Labor |
| Charlestown | Andrew Cornwell | | Liberal | Resigned due to ICAC investigation | 25 October 2014 | Jodie Harrison | | Labor |
| Miranda | Graham Annesley | | Liberal | Resigned to become CEO of Gold Coast Titans rugby league team | 19 October 2013 | Barry Collier | | Labor |
| Northern Tablelands | Richard Torbay | | Independent | Resigned | 25 May 2013 | Adam Marshall | | National |
| Sydney | Clover Moore | | Independent | Resigned due to new state laws preventing dual membership of state parliament and local council | 27 October 2012 | Alex Greenwich | | Independent |
| Heffron | Kristina Keneally | | Labor | Resigned after being appointed CEO of Basketball Australia | 25 August 2012 | Ron Hoenig | | Labor |
| Clarence | Steve Cansdell | | National | Resigned after falsifying a statutory declaration regarding a speeding offence | 19 November 2011 | Chris Gulaptis | | National |
| Fifty-fourth Legislative Assembly 2007–2011 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Penrith | Karyn Paluzzano | | Labor | Resigned after misleading ICAC | 19 June 2010 | Stuart Ayres | | Liberal |
| Ryde | John Watkins | | Labor | Resigned to spend time with family | 18 October 2008 | Victor Dominello | | Liberal |
| Port Macquarie | Rob Oakeshott | | Independent | Resigned to contest federal Lyne by-election | 18 October 2008 | Peter Besseling | | Independent |
| Lakemba | Morris Iemma | | Labor | Resigned after losing confidence of caucus | 18 October 2008 | Robert Furolo | | Labor |
| Cabramatta | Reba Meagher | | Labor | Resigned after being dismissed from cabinet | 18 October 2008 | Nick Lalich | | Labor |
| Fifty-third Legislative Assembly 2003–2007 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Pittwater | John Brogden | | Liberal | Ill health | 26 November 2005 | Alex McTaggart | | Independent |
| Macquarie Fields | Craig Knowles | | Labor | Resigned after it became apparent that he would not become Premier | 17 September 2005 | Steven Chaytor | | Labor |
| Maroubra | Bob Carr | | Labor | Resigned as Premier | 17 September 2005 | Michael Daley | | Labor |
| Marrickville | Andrew Refshauge | | Labor | Resigned as Deputy Premier | 17 September 2005 | Carmel Tebbutt | | Labor |
| Dubbo | Tony McGrane | | Independent | Death | 20 November 2004 | Dawn Fardell | | Independent |
| Fifty-second Legislative Assembly 1999–2003 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Hornsby | Stephen O'Doherty | | Liberal | Resigned | 23 February 2002 | Judy Hopwood | | Liberal |
| Tamworth | Tony Windsor | | Independent | Resigned to contest federal seat of New England at 2001 election | 8 December 2001 | John Cull | | National |
| Auburn | Peter Nagle | | Labor | Ill health | 8 September 2001 | Barbara Perry | | Labor |
| Campbelltown | Michael Knight | | Labor | Resigned after completion of term as Olympics Minister | 3 February 2001 | Graham West | | Labor |
| Fifty-first Legislative Assembly 1995–1999 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Sutherland | Chris Downy | | Liberal | Resigned | 12 February 1997 | Lorna Stone | | Liberal |
| Port Macquarie | Wendy Machin | | National | Resigned | 30 November 1996 | Rob Oakeshott | | National |
| Clarence | Ian Causley | | National | Resigned to contest federal seat of Page at the 1996 election | 25 May 1996 | Harry Woods | | Labor |
| Orange | Garry West | | National | Resigned | 25 May 1996 | Russell Turner | | National |
| Pittwater | Jim Longley | | Liberal | Resigned | 25 May 1996 | John Brogden | | Liberal |
| Southern Highlands | John Fahey | | Liberal | Resigned to contest federal seat of Macarthur at the 1996 election | 25 May 1996 | Peta Seaton | | Liberal |
| Strathfield | Paul Zammit | | Liberal | Resigned to contest federal seat of Lowe at the 1996 election | 25 May 1996 | Bruce MacCarthy | | Liberal |
| Fiftieth Legislative Assembly 1991–1995 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Cabramatta | John Newman | | Labor | Assassinated by Phuong Ngo | 22 October 1994 | Reba Meagher | | Labor |
| Parramatta | Andrew Ziolkowski | | Labor | Death | 27 August 1994 | Gabrielle Harrison | | Labor |
| Vaucluse | Michael Yabsley | | Liberal | Resigned | 9 April 1994 | Peter Debnam | | Liberal |
| North Shore | Phillip Smiles | | Liberal | Resigned | 5 February 1994 | Jillian Skinner | | Liberal |
| The Hills | Tony Packard | | Liberal | Resigned after involvement in a business scandal | 28 August 1993 | Michael Richardson | | Liberal |
| Gordon | Tim Moore | | Liberal | Resigned (see Metherell affair) | 22 August 1992 | Jeremy Kinross | | Liberal |
| Ku-ring-gai | Nick Greiner | | Liberal | Resigned after losing Premiership (see Metherell affair) | 22 August 1992 | Stephen O'Doherty | | Liberal |
| Davidson | Terry Metherell | | Independent | Accepted an appointment in the public service (see Metherell affair) | 2 May 1992 | Andrew Humpherson | | Liberal |
| The Entrance | Bob Graham | | Liberal | Result overturned by the Court of Disputed Returns | 18 January 1992 | Grant McBride | | Labor |
| Forty-ninth Legislative Assembly 1988–1991 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Coffs Harbour | Matt Singleton | | National | Resigned | 3 November 1990 | Andrew Fraser | | National |
| Macquarie Fields | Stan Knowles | | Labor | Resigned | 3 November 1990 | Craig Knowles | | Labor |
| The Hills | Fred Caterson | | Liberal | Resigned | 1 September 1990 | Tony Packard | | Liberal |
| Granville | Laurie Ferguson | | Labor | Successfully contested the federal seat of Reid at the 1990 election | 23 June 1990 | Kim Yeadon | | Labor |
| Heffron | Laurie Brereton | | Labor | Successfully contested the federal seat of Kingsford-Smith at the 1990 election | 23 June 1990 | Deirdre Grusovin | | Labor |
| Smithfield | Janice Crosio | | Labor | Successfully contested the federal seat of Prospect at the 1990 election | 23 June 1990 | Carl Scully | | Labor |
| Liverpool | George Paciullo | | Labor | Resigned after being passed over as leader of the party | 29 April 1989 | Peter Anderson | | Labor |
| Wallsend | Ken Booth | | Labor | Death | 17 December 1988 | John Mills | | Labor |
| North Shore | Ted Mack | | Independent | Resigned | 5 November 1988 | Robyn Read | | Independent |
| Port Stephens | Bob Martin | | Labor | Result voided by the Court of Disputed Returns | 5 November 1988 | Bob Martin | | Labor |
| Vaucluse | Ray Aston | | Liberal | Death | (6 June 1988)* | Michael Yabsley | | Liberal |
| Although the Vaucluse by-election was set for 18 June 1988, Michael Yabsley was declared elected unopposed on the close of nominations on 6 June. Forty-eighth Legislative Assembly 1984–1988 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Northern Tablelands | Bill McCarthy | | Labor | Resignation due to ill health, dying 3 days later | 23 May 1987 | Ray Chappell | | National |
| Bankstown | Ric Mochalski | | Labor | Resigned after being charged with fraud | 31 January 1987 | Doug Shedden | | Labor |
| Heathcote | Rex Jackson | | Labor | Resigned amidst a corruption scandal that ultimately led to his imprisonment | 31 January 1987 | Ian McManus | | Labor |
| Rockdale | Brian Bannon | | Labor | Accepted a government position and created a seat for the Premier | 2 August 1986 | Barrie Unsworth | | Labor |
| Bass Hill | Neville Wran | | Labor | Resigned | 2 August 1986 | Michael Owen | | Liberal |
| Pittwater | Max Smith | | Independent | Resigned | 31 May 1986 | Jim Longley | | Liberal |
| Vaucluse | Rosemary Foot | | Liberal | Resigned | 31 May 1986 | Ray Aston | | Liberal |
| Kiama | Bill Knott | | Labor | Resigned | 1 February 1986 | Bob Harrison | | Labor |
| Canterbury | Kevin Stewart | | Labor | Accepted position as Agent-General in London | 1 February 1986 | Kevin Moss | | Labor |
| Cabramatta | Eric Bedford | | Labor | Resigned | 1 February 1986 | John Newman | | Labor |
| Gloucester | Leon Punch | | National | Resigned | 12 October 1985 | Wendy Machin | | National |
| Peats | Paul Landa | | Labor | Death | 2 February 1985 | Tony Doyle | | Labor |
| Murray | Tim Fischer | | National | Successfully contested the seat of Farrer at the 1984 federal election | 2 February 1985 | Jim Small | | National |
| Forty-seventh Legislative Assembly 1981–1984 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Maroubra | Bill Haigh | | Labor | Resigned after losing cabinet position | 22 October 1983 | Bob Carr | | Labor |
| Marrickville | Tom Cahill | | Labor | Death | 22 October 1983 | Andrew Refshauge | | Labor |
| Riverstone | Tony Johnson | | Labor | Resigned | 22 October 1983 | Richard Amery | | Labor |
| Kogarah | Bill Crabtree | | Labor | Resigned after losing cabinet position | 22 October 1983 | Brian Langton | | Labor |
| Drummoyne | Michael Maher | | Labor | Successfully contested the federal seat of Lowe at the 1982 Lowe by-election | 17 April 1982 | John Murray | | Labor |
| Forty-sixth Legislative Assembly 1978–1981 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Cessnock | Bob Brown | | Labor | Successfully contested the federal seat of Hunter at the 1980 election | 21 February 1981 | Stan Neilly | | Labor |
| Maitland | Milton Morris | | Liberal | Unsuccessfully contested the federal seat of Lyne at the 1980 election | 21 February 1981 | Peter Toms | | Liberal |
| Oxley | Bruce Cowan | | National Country | Successfully contested the federal seat of Lyne at the 1980 election | 21 February 1981 | Peter King | | National Country |
| Sturt | Tim Fischer | | National Country | Resigned to successfully contest the seat of Murray at the 1980 Murray by-election | 21 February 1981 | John Sullivan | | National Country |
| Bankstown | Nick Kearns | | Labor | Death | 13 September 1980 | Ric Mochalski | | Labor |
| Ku-ring-gai | John Maddison | | Liberal | Resigned | 13 September 1980 | Nick Greiner | | Liberal |
| Murray | Mary Meillon | | Liberal | Death | 13 September 1980 | Tim Fischer | | National Country |
| Castlereagh | Jack Renshaw | | Labor | Resigned | 23 February 1980 | Jim Curran | | Labor |
| Forty-fifth Legislative Assembly 1976–1978 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Earlwood | Eric Willis | | Liberal | Resigned | 15 July 1978 | Ken Gabb | | Labor |
| The Hills | Max Ruddock | | Liberal | Resigned | 9 October 1976 | Fred Caterson | | Liberal |
| Forty-fourth Legislative Assembly 1973–1976 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Orange | Charles Cutler | | National Country | Resigned | 14 February 1976 | Garry West | | National Country |
| Wagga Wagga | Wal Fife | | Liberal | Resigned to contest the federal seat of Farrer at the next election | 6 December 1975 | Joe Schipp | | Liberal |
| Lane Cove | Ken McCaw | | Liberal | Resigned | 8 February 1975 | John Dowd | | Liberal |
| Pittwater | Robert Askin | | Liberal | Resigned | 8 February 1975 | Bruce Webster | | Liberal |
| Coogee | Ross Freeman | | Liberal | Result voided by the Court of Disputed Returns | 20 July 1974 | Michael Cleary | | Labor |
| Goulburn | Ron Brewer | | National Country | Unsuccessfully contested the federal seat of Eden-Monaro at the 1974 federal election | 20 July 1974 | Ron Brewer | | National Country |
| Forty-third Legislative Assembly 1971–1973 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Murray | Joe Lawson | | Independent | Death | 6 October 1973 | Mary Meillon | | Liberal |
| Byron | Stanley Stephens | | Country | Resigned | 17 February 1973 | Jack Boyd | | Country |
| Armidale | Davis Hughes | | Country | Accepted position as Agent-General in London | 17 February 1973 | David Leitch | | Country |
| Hawkesbury | Bernie Deane | | Liberal | Resigned | 17 February 1973 | Kevin Rozzoli | | Liberal |
| Charlestown | Jack Stewart | | Labor | Death | 18 November 1972. | Richard Face | | Labor |
| Mosman | Pat Morton | | Liberal | Resigned | 29 July 1972 | David Arblaster | | Liberal |
| Forty-second Legislative Assembly 1968–1971 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Georges River | Douglas Cross | | Liberal | Death | 19 September 1970 | Frank Walker | | Labor |
| Murrumbidgee | Al Grassby | | Labor | Successfully contested the federal seat of Riverina at the 1969 federal election | 14 February 1970 | Lin Gordon | | Labor |
| Randwick | Lionel Bowen | | Labor | Successfully contested the federal seat of Kingsford Smith at the 1969 federal election | 14 February 1970 | Laurie Brereton | | Labor |
| Upper Hunter | Frank O'Keefe | | Country | Successfully contested the federal seat of Paterson at the 1969 federal election | 14 February 1970 | Col Fisher | | Country |
| Lake Macquarie | Jim Simpson | | Labor | Death | 9 April 1969 | Merv Hunter | | Labor |
| Forty-first Legislative Assembly 1965–1968 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Bathurst | Gus Kelly | | Labor | Death | 6 May 1967 | Clive Osborne | | Country |
| Oxley | Les Jordan | | Liberal | Death | 6 November 1965 | Bruce Cowan | | Country |
| Bondi | Abe Landa | | Labor | Accepted the position of state Agent-General in London | 6 November 1965 | Syd Einfeld | | Labor |
| Fortieth Legislative Assembly 1962–1965 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Lakemba | Stan Wyatt | | Labor | Death | 19 September 1964 | Vince Durick | | Labor |
| Waratah | Edward Greaves | | Labor | Death | 8 August 1964 | Frank Purdue | | Independent |
| Wollongong-Kembla | Rex Connor | | Labor | Successfully contested the federal seat of Cunningham at the 1963 election | 29 February 1964 | Doug Porter | | Labor |
| Casino | Ian Robinson | | Country | Successfully contested the federal seat of Cowper at the 1963 election | 29 February 1964 | Richmond Manyweathers | | Country |
| Thirty-ninth Legislative Assembly 1959–1962 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Liverpool Plains | Roger Nott | | Labor | Accepted an appointment as Administrator of the Northern Territory | 25 March 1961 | Frank O'Keefe | | Country |
| Paddington-Waverley | William Ferguson | | Labor | Death | 25 February 1961 | Keith Anderson | | Labor |
| Temora | Doug Dickson | | Country | Death | 8 October 1960 | Jim Taylor | | Country |
| Kurri Kurri | George Booth | | Labor | Death | 8 October 1960 | Ken Booth | | Labor |
| Cook's River | Joseph Cahill | | Labor | Death | 12 December 1959 | Tom Cahill | | Labor |
| Lismore | Jack Easter | | Country | Result voided by the Court of Disputed Returns | 12 September 1959. | Keith Compton | | Labor |
| Thirty-eighth Legislative Assembly 1956–1959 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Wagga Wagga | Eddie Graham | | Labor | Death | 14 December 1957 | Wal Fife | | Liberal |
| Wollondilly | Blake Pelly | | Liberal | Resigned | 26 October 1957 | Tom Lewis | | Liberal |
| Vaucluse | Murray Robson | | Liberal | Resigned | 24 August 1957 | Geoffrey Cox | | Liberal |
| Kahibah | Tom Armstrong | | Independent Labor | Death | 13 April 1957 | Jack Stewart | | Labor |
| Burwood | Leslie Parr | | Liberal | Death | 16 February 1957 | Ben Doig | | Liberal |
| Thirty-seventh Legislative Assembly 1953–1956 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Bulli | Laurie Kelly Sr. | | Labor | Death | 9 July 1955 | Rex Jackson | | Labor |
| Clarence | Cecil Wingfield | | Country | Death | 26 March 1955 | Bill Weiley | | Country |
| Phillip | Tom Shannon | | Labor | Death | 14 August 1954 | Pat Hills | | Labor |
| Leichhardt | Claude Matthews | | Labor | Committed suicide | 20 March 1954 | Reg Coady | | Labor |
| Kahibah | Joshua Arthur | | Labor | Resigned after being expelled from the Labor Party, following adverse findings into his conduct by a Royal Commission | 31 October 1953 | Tom Armstrong | | Independent Labor |
| Waverley | Clarrie Martin | | Labor | Death | 31 October 1953 | William Ferguson | | Labor |
| Dulwich Hill | George Weir | | Labor | Appointed to the Industrial Relations Commission of New South Wales | 20 June 1953 | Cliff Mallam | | Labor |
| Thirty-sixth Legislative Assembly 1950–1953 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Ashfield | Athol Richardson | | Liberal | Accepted an appointment as a Judge of the Supreme Court | 28 June 1952 | Jack Richardson | | Labor |
| Liverpool | James McGirr | | Labor | Appointed chair of the Maritime Services Board | 24 May 1952 | Jack Mannix | | Labor |
| Neutral Bay | Ivan Black | | Liberal | Unsuccessfully contested preselection for the federal seat of Warringah at the 1951 election | (21 May 1951) | Ivan Black | | Liberal |
| Burwood | Gordon Jackett | | Liberal | Death | 2 June 1951 | Leslie Parr | | Liberal |
| Thirty-fifth Legislative Assembly 1947–1950 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Concord | Brice Mutton | | Liberal | Death | 11 February 1950 | John Adamson | | Liberal |
| Wollongong-Kembla | Billy Davies | | Labor | Successfully contested the seat of Cunningham at the 1949 federal election | 11 February 1950 | Baden Powell | | Labor |
| Armidale | David Drummond | | Country | Successfully contested the seat of New England at the 1949 federal election | 11 February 1950 | Davis Hughes | | Country |
| Wollondilly | Jeff Bate | | Liberal | Successfully contested the seat of Macarthur at the 1949 federal election | (23 January 1950) | Blake Pelly | | Liberal |
| Cessnock | Jack Baddeley | | Labor | Accepted an appointment as Chairman of the State Coal Mine Authority | 8 October 1949 | John Crook | | Labor |
| Redfern | George Noble | | Labor | Death | 8 October 1949 | Kevin Dwyer | | Labor |
| Concord | Bill Carlton | | Labor | Death | 12 March 1949 | Brice Mutton | | Liberal |
| Cobar | Mat Davidson | | Labor | Death | 12 March 1949 | Ernest Wetherell | | Labor |
| Kogarah | William Currey | | Labor | Death | 17 July 1948 | Douglas Cross | | Liberal |
| Coogee | Lou Cunningham | | Labor | Death | 8 May 1948 | Kevin Ellis | | Liberal |
| Hartley | Hamilton Knight | | Labor | Accepted an appointment to the Commonwealth Industrial Commission | 13 December 1947 | Jim Chalmers | | Labor |
| Thirty-fourth Legislative Assembly 1944–1947 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Corowa | Christopher Lethbridge | | Liberal | Unsuccessfully contested the federal seat of Riverina at the 1946 federal election | 9 November 1946 | Ebenezer Kendell | | Country |
| Ashfield | Athol Richardson | | Liberal | Unsuccessfully contested the federal seat of Parkes at the 1946 federal election | 9 November 1946 | Athol Richardson | | Liberal |
| Auburn | Jack Lang | | Lang Labor | Successfully contested the federal seat of Reid at the 1946 federal election | 9 November 1946 | Chris Lang | | Lang Labor |
| Albury | Alexander Mair | | Liberal | Unsuccessfully contested a seat in the Australian Senate at the 1946 federal election | 9 November 1946 | John Hurley | | Labor |
| Goulburn | Jack Tully | | Labor | Resigned | 1 June 1946 | Laurie Tully | | Labor |
| Neutral Bay | Reginald Weaver | | Liberal | Death | 15 December 1945 | Ivan Black | | Liberal |
| Manly | Alfred Reid | | Liberal | Death | 15 September 1945 | Douglas Darby | | Liberal |
| Blacktown | Frank Hill | | Labor | Death | 18 August 1945 | John Freeman | | Labor |
| Ryde | James Shand | | Independent Democrat | Death | 3 February 1945 | Eric Hearnshaw | | Liberal |
| Thirty-third Legislative Assembly 1941–1944 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Auburn | Jack Lang | | Lang Labor | Unsuccessfully contested the federal seat of Reid at the 1943 election | 2 October 1943 | Jack Lang | | Lang Labor |
| Lachlan | Griffith Evans | | Country | Death | 25 September 1943 | John Chanter | | Labor |
| Willoughby | Edward Sanders | | UAP | Death | 25 September 1943 | George Brain | | UAP |
| South Coast | Rupert Beale | | Independent | Death | 14 November 1942 | Jack Beale | | Independent |
| Dubbo | George Wilson | | Country | Death | 6 June 1942 | Clarrie Robertson | | Labor |
| Thirty-second Legislative Assembly 1938–1941 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Barwon | Ben Wade | | Country | Unsuccessfully contest the federal seat of Gwydir at the 1940 election | 16 November 1940 | Roy Heferen | | Labor |
| Ryde | Eric Spooner | | UAP | Successfully contested the federal seat of Robertson at the 1940 election | 14 September 1940 | Arthur Williams | | Labor |
| Croydon | Bertram Stevens | | UAP | Unsuccessfully contested the federal seat of Lang at the 1940 election | 7 September 1940 | David Hunter | | UAP |
| Tamworth | Frank Chaffey | | UAP | Death | 10 August 1940 | Bill Chaffey | | UAP |
| Upper Hunter | Malcolm Brown | | Country | Death | 7 October 1939 | D'Arcy Rose | | Country |
| Waverley | John Waddell | | UAP | Death | 22 April 1939 | Clarrie Martin | | Industrial Labor |
| Hurstville | James Webb | | UAP | Death | 18 March 1939 | Clive Evatt | | Industrial Labor |
| Balmain | John Quirk | | Labor | Death | 14 January 1939 | Mary Quirk | | Labor |
| Wollondilly | Mark Morton | | UAP | Death | 12 November 1938 | Jeff Bate | | UAP |
| Gordon | Harry Turner | | UAP | Result voided by Court of Disputed Returns | 24 September 1938 | Harry Turner | | UAP |
| Coogee | John Dunningham | | UAP | Death | 25 June 1938 | Thomas Mutch | | UAP |
| Thirty-first Legislative Assembly 1935–1938 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Corowa | Richard Ball | | Country | Death | 11 December 1937 | Christopher Lethbridge | | Independent |
| Gordon | Philip Goldfinch | | UAP | Resigned (Increased commitment to business interests) | 7 August 1937 | Harry Turner | | UAP |
| Woollahra | Daniel Levy | | UAP | Death | 26 June 1937 | Harold Mason | | Independent UAP |
| Vaucluse | William Foster | | UAP | Death | 29 August 1936 | Murray Robson | | Independent UAP |
| Gordon | Thomas Bavin | | UAP | Accepted an appointment as a Judge of the Supreme Court | (23 November 1935) | Philip Goldfinch | | UAP |
| Thirtieth Legislative Assembly 1932–1935 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Leichhardt | Joe Lamaro | | Labor (NSW) | Unsuccessfully contested the federal seat of Watson at the 1934 election | 20 October 1934 | Claude Matthews | | Labor (NSW) |
| Gloucester | Walter Bennett | | UAP | Death | 25 August 1934 | Charles Bennett | | UAP |
| Hamilton | Hugh Connell | | Labor (NSW) | Death | 24 February 1934 | William Brennan | | Labor (NSW) |
| Annandale | Robert Stuart-Robertson | | Labor (NSW) | Death | 24 June 1933 | Bob Gorman | | Labor (NSW) |
| Bulli | Andrew Lysaght, junior | | Labor (NSW) | Death | 3 June 1933 | John Sweeney | | Labor (NSW) |
| Lismore | William Missingham | | Country | Death | 11 March 1933 | William Frith | | Country |
| Leichhardt | Barney Olde | | Labor (NSW) | Death | 10 December 1932 | Joe Lamaro | | Labor (NSW) |
| Twenty-ninth Legislative Assembly 1930–1932 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Upper Hunter | William Cameron | | Nationalist | Death | 13 June 1931 | Malcolm Brown | | Independent Country |
| Annandale | Robert Stuart-Robertson | | Labor (NSW) | Insolvency | 25 April 1931 | Robert Stuart-Robertson | | Labor (NSW) |
| Clarence | Alfred Pollack | | Country | Death | 7 March 1931 | Alfred Henry | | Country |
| Twenty-eighth Legislative Assembly 1927–1930 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Lane Cove | Bryce Walmsley | | Nationalist | Death | 26 July 1930 | Herbert FitzSimons | | Nationalist |
| Ashfield | Milton Jarvie | | Nationalist | Resigned after being implicated in a bribery scandal | 5 October 1929 | Milton Jarvie | | Nationalist |
| Parramatta | Albert Bruntnell | | Nationalist | Death | 23 February 1929 | Herbert Lloyd | | Nationalist |
| Coogee | Hyman Goldstein | | Nationalist | Death – probably murdered by ex-MLA Tom Ley | 22 September 1928 | John Dunningham | | Nationalist |
| Hamilton | David Murray | | Labor | Death | 8 September 1928 | James Smith | | Labor |
| Wollondilly | George Fuller | | Nationalist | Accepted position as Agent-General in London in February 1928 | 3 March 1928 | Mark Morton | | Nationalist |
| Twenty-seventh Legislative Assembly 1925–1927 The 25th, 26th and 27th Legislative Assemblies were elected using a form of proportional representation with multi-member seats and a single transferable vote (modified Hare-Clark). Under the provisions of the Parliamentary Elections (Casual Vacancies) Act, casual vacancies were filled by the next unsuccessful candidate on the incumbent member's party list. If an Independent member retired, the Clerk of the Assembly determined who would fill the vacancy based on the departing members voting record in questions of confidence. The date listed as the by-election date is the day on which the new member was sworn into the Assembly. |||||||||
| Electorate | Incumbent | Party | Party | Reason for vacancy | Date of appointment | Person appointed | Party | Party |
| Cumberland | William FitzSimons | | Nationalist | Death | (22 September 1926) | James Shand | | Nationalist |
| North Shore | Alick Kay ¶ | | Independent | Accepted a position on the Metropolitan Meat Board. | (22 September 1926) | Arthur Tonge | | Labor |
| Goulburn | John Perkins | | Nationalist | Resigned to successfully contest the federal seat of Eden-Monaro at the 1926 Eden-Monaro by-election. | (21 January 1926) | Henry Bate | | Nationalist |
| St George | Thomas Ley | | Nationalist | Resigned to successfully contest the federal seat of Barton at the 1925 election | (30 September 1925) | William Bagnall | | Nationalist |
| Sydney | John Birt | | Labor | Death | (24 June 1925) | Patrick Minahan | | Labor |
| ¶ Kay had supported the Lang Government in votes of confidence in the Assembly, the Clerk of the Parliament therefore named the first unsuccessful Labor candidate in the North Shore electorate as his replacement. Twenty-sixth Legislative Assembly 1922–1925 |||||||||
| Electorate | Incumbent | Party | Party | Reason for vacancy | Date of appointment | Person appointed | Party | Party |
| North Shore | Arthur Cocks | | Nationalist | Accepted position of Agent-General in London | (24 March 1925) | Alfred Reid | | Nationalist |
| Namoi | Patrick Scully | | Labor | Resigned | (20 September 1923) | William Scully | | Labor |
| Sturt | Jabez Wright | | Labor | Death | (30 September 1922) | Ted Horsington | | Labor |
| Wammerawa | William Ashford | | Independent | Result overturned (Change of member without by-election) | (26 July 1922) | Joseph Clark | | Labor |
| Twenty-fifth Legislative Assembly 1920–1922 |||||||||
| Electorate | Incumbent | Party | Party | Reason for vacancy | Date of appointment | Person appointed | Party | Party |
| Goulburn ‡ | William Millard | | Nationalist | Death | (22 November 1921) | John Perkins | | Nationalist |
| Balmain | John Storey | | Labor | Death | (18 October 1921) | Tom Keegan | | Labor |
| Newcastle | William Kearsley | | Labor | Death | (30 August 1921) | David Murray | | Labor |
| Sturt ¶ | Percy Brookfield | | Socialist Labor | Murdered while trying to disarm a deranged man at Riverton | (30 August 1921) | Jabez Wright | | Labor |
| Oxley | George Briner | | Progressive | Death | (15 December 1920) | Theodore Hill | | Progressive |
| Eastern Suburbs | James Fingleton | | Labor | Death | (15 December 1920) | Daniel Dwyer | | Labor |
| Goulburn | Gus James | | Nationalist | Accepted an appointment as a Judge of the Supreme Court | (15 December 1920) | William Millard | | Nationalist |
| Murray | George Beeby | | Progressive | Accepted a judicial appointment | (15 December 1920) | Matthew Kilpatrick | | Progressive |
| ¶ The Speaker had received correspondence nominating two unsuccessful candidates from the 1920 election, Thomas Hynes and John O'Reilly. However, the terms of the Parliamentary Elections (Casual Vacancies) Act stated that a nomination to fill the vacancy had to come from a recognised party leader. Labor leader and Premier John Storey nominated Jabez Wright. ‡Millard had been appointed to replace Gus James and, as there were no further unsuccessful Nationalist candidates, the Parliamentary Elections (Casual Vacancies) Act was amended to allow his replacement by another Nationalist supporter. Twenty-fourth Legislative Assembly 1917–1920 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Paddington | Lawrence O'Hara | | Labor | Death | 26 July 1919 | John Birt | | Labor |
| Paddington | John Osborne | | Labor | Accepted as appointment to the Metropolitan Meat Board | 24 May 1919 | Lawrence O'Hara | | Labor |
| Petersham | John Cohen | | Nationalist | Accepted an appointment as a Judge of the District Court | 22 March 1919 | Sydney Shillington | | Nationalist |
| Monaro | Gus Miller | | Labor | Death | 23 November 1918 | John Bailey | | Labor |
| Upper Hunter | Mac Abbott | | Nationalist | Resigned | 8 June 1918 | William Cameron | | Nationalist |
| Cobar | Charles Fern | | Labor | Death | (1 June 1918) | Mat Davidson | | Labor |
| Gloucester | Richard Price | | Independent Liberal | Expelled after a Royal Commission found he had made "wanton lies" in an attack on the Lands Minister William Ashford | 10 November 1917 | Richard Price | | Independent Liberal |
| Murray | Robert Scobie | | Nationalist | Death | 22 September 1917 | Brian Doe | | Nationalist |
| Macquarie | Thomas Thrower | | Labor | Death | 12 July 1917 | Patrick McGirr | | Labor |
| Twenty-third Legislative Assembly 1913–1917 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Sturt | John Cann | | Labor | Accepted the position of Commissioner of Railways | 3 February 1917 | Percy Brookfield | | Labor |
| Bingara | George McDonald | | Labor | Resigned from Labor after the 1916 NSW Labor Conference passed a motion of no confidence in the Holman government | 10 June 1916 | George McDonald | | Independent Labor |
| Parramatta | Tom Moxham | | Liberal Reform | Death | 12 February 1916 | Albert Bruntnell | | Liberal Reform |
| Drummoyne | George Richards | | Liberal Reform | Death | 22 January 1916 | Alexander Graff | | Liberal Reform |
| Willoughby | Edward Larkin | | Labor | Died on active service on 25 April 1915 | 25 September 1915 | John Haynes | | Independent |
| Wollondilly | Frank Badgery | | Liberal Reform | Death | (2 October 1915) | George Fuller | | Liberal Reform |
| Armidale | George Braund | | Liberal Reform | Died on active service | (18 September 1915) | Herbert Lane | | Liberal Reform |
| Clarence | John McFarlane | | Liberal Reform | Death | 14 August 1915 | William Zuill | | Independent Liberal |
| Castlereagh | John Treflé | | Labor | Death | 20 February 1915 | Guy Arkins | | Labor |
| Canterbury | Henry Peters | | Labor | Bankrupt | 10 October 1914 | George Cann | | Labor |
| Twenty-second Legislative Assembly 1910–1913 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Wollondilly | William McCourt | | Liberal Reform | Death | 19 July 1913 | Frank Badgery | | Liberal Reform |
| Blayney | George Beeby | | Labor | Resigned from the ministry, parliament and party in protest at the power of the extra-parliamentary Labor Party executive | 23 January 1913 | George Beeby | | Independent |
| Alexandria | John Dacey | | Labor | Death | 18 May 1912 | Simon Hickey | | Labor |
| Maitland | John Gillies | | Independent Liberal | Death | 28 October 1911 | Charles Edward Nicholson | | Liberal Reform |
| Yass | Niels Nielson | | Labor | ¶ | 5 March 1913 | Greg McGirr | | Labor |
| Cobar | Donald Macdonell | | Labor | ¶ | (16 December 1911) | Charles Fern | | Labor |
| Cobar | Donald Macdonell | | Labor | ¶ | (7 October 1911) | Donald Macdonell | | Labor |
| Liverpool Plains | John Perry | | Liberal Reform | ¶ | 28 October 1911 | William Ashford | | Labor |
| Liverpool Plains | Henry Hoyle | | Labor | ¶ | 16 August 1911 | John Perry | | Liberal Reform |
| Mudgee | Bill Dunn | | Labor | ¶ | 16 August 1911 | Bill Dunn | | Labor |
| ¶ Mudgee Labor MLA Bill Dunn and Liverpool Plains Labor MLA Henry Hoyle resigned from the Labor Party and Parliament on 25 July 1911 in protest at legislation on land ownership introduced by Lands Minister, Niels Nielson. As a result, Labor was left without a majority in the house and rather than face a vote of no confidence, the Ministry and Speaker resigned. This forced the House to be prorogued with the result that Cobar Labor MLA, Donald Macdonell, who was unwell but expected to recover, was automatically expelled for non-attendance during an entire session. By the time of the subsequent by-elections, Labor policy had been reversed and Nielsen had left the ministry. Dunn rejoined the party and successfully re-contested, the Mudgee by-election on 16 August 1911. Hoyle did not re-contest the Liverpool Plains by-election which was won by Liberal candidate, John Perry by three votes on the same day. This result was overturned on appeal and at the second by-election on 28 October, Labor candidate, William Ashford was successful. In Cobar, Macdonell was unopposed when re-elected on 7 October, but died three weeks later. The Labor candidate, Charles Fern was unopposed at the second by-election on 16 December. Denied further ministerial appointment Nielsen resigned from the seat of Yass and Labor candidate Greg McGirr won the resultant by-election on 19 July 1913. Twenty-first Legislative Assembly 1907–1910 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Belmore | Edward O'Sullivan | | Labor | Death | 21 May 1910 | Patrick Minahan | | Labor |
| Darling Harbour | John Norton | | Independent | Resigned to unsuccessfully contest a Senate seat at the 1910 election | 13 April 1910 | John Cochran | | Labor |
| Queanbeyan | Granville Ryrie | | Liberal Reform | Resigned to unsuccessfully contest the federal seat of Werriwa at the 1910 election | 13 April 1910 | John Cusack | | Labor |
| Upper Hunter | William Fleming | | Liberal Reform | Resigned to unsuccessfully contest the federal seat of New England at the 1910 election | 13 April 1910 | William Ashford | | Labor |
| Northumberland | Matthew Charlton | | Labor | Resigned to successfully contest the federal seat of Hunter at the 1910 election | (23 March 1910) | William Kearsley | | Labor |
| Sturt | Arthur Griffith | | Labor | Resigned from parliament after a dispute with the Speaker | (21 November 1908) | Arthur Griffith | | Labor |
| St George | Joseph Carruthers | | Liberal Reform | Resigned | 20 May 1908 | William Taylor | | Liberal Reform |
| Twentieth Legislative Assembly 1904–1907 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Blayney | Paddy Crick | | Progressive | Resigned after being acquitted of corruption charges | 12 January 1907 | John Withington | | Liberal Reform |
| Castlereagh | Hugh Macdonald | | Labor | Death | 24 November 1906 | John Treflé | | Labor |
| Surry Hills | John Norton | | Independent | Challenged William Holman to face a by-election | 21 July 1906 | Albert Bruntnell | | Liberal Reform |
| Cootamundra | William Holman | | Labor | Challenged to a by-election by John Norton | 17 July 1906 | William Holman | | Labor |
| Queanbeyan | Alan Millard | | Liberal Reform | Criminal conviction: Fraud | 7 April 1906 | Granville Ryrie | | Liberal Reform |
| Ashfield | Frederick Winchcombe | | Liberal Reform | Extended absence visiting England | 16 August 1905 | William Robson | | Liberal Reform |
| Rous | John Coleman | | Liberal Reform | Death | 11 February 1905 | George Hindmarsh | | Liberal Reform |
| Nineteenth Legislative Assembly 1901–1904 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Ryde | Frank Farnell | | Independent Liberal | Appointment to Fisheries Board | 23 January 1904 | Edward Terry | | Independent Liberal |
| Illawarra | Archibald Campbell | | Liberal Reform | Death | 9 January 1904 | Edward Allen | | Liberal Reform |
| Moree | William Webster | | Labor | Successful candidate for Gwydir at federal election | 12 December 1903 | Percy Stirton | | Liberal Reform |
| Armidale | Edmund Lonsdale | | Liberal Reform | Successful candidate for New England at federal election | 12 December 1903 | Sydney Kearney | | Liberal Reform |
| Waratah | Arthur Griffith | | Labor | Unsuccessful candidate for Senate at federal election | 5 December 1903 | Matthew Charlton | | Labor |
| Glen Innes | Francis Wright | | Progressive | Death | 28 October 1903 | Follett Thomas | | Liberal Reform |
| Willoughby | George Howarth | | Liberal Reform | Bankruptcy | 9 September 1903 | Charles Wade | | Liberal Reform |
| Tamworth | Raymond Walsh | | Progressive | Bankruptcy | 4 April 1903 | John Garland | | Liberal Reform |
| Balmain South | Sydney Law | | Labor | Refused Caucus solidarity pledge | 6 December 1902 | Sydney Law | | Independent Labor |
| Inverell | William McIntyre | | Progressive | Death | 31 May 1902 | George Jones | | Labor |
| Sydney-Pyrmont | Samuel Smith | | Labor | Appointment to Court of Arbitration | 24 May 1902 | John McNeill | | Labor |
| Condoublin | Patrick Clara | | Labor | Election overturned by the Elections and Qualifications Committee | 4 November 1901 | Patrick Clara | | Labor |
| Eighteenth Legislative Assembly 1898–1901 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Hume | William Lyne | | Protectionist | Successfully contested Hume at 1901 Federal election | 17 April 1901 | Gordon McLaurin | | Protectionist |
| Ashfield | Bernhard Wise | | Protectionist | Appointed to Legislative Council | 10 November 1900 | Frederick Winchcombe | | Free Trade |
| Uralla-Walcha | William Piddington | | Protectionist | Death | 27 October 1900 | Michael MacMahon | | Protectionist |
| Bourke | William Davis | | Protectionist | Resignation due to insolvency | (6 September 1900) | William Davis | | Protectionist |
| Canterbury | Sydney Smith | | Free Trade | By-election result voided by the Elections and Qualifications Committee | 28 July 1900 | Thomas Taylor | | Independent |
| Bathurst | Francis Suttor | | Protectionist | Appointed to Legislative Council | 25 June 1900 | William Young | | Protectionist |
| Canterbury | Varney Parkes | | Free Trade | Resignation | 9 June 1900 | Sydney Smith | | Free Trade |
| Uralla-Walcha | William Piddington | | Protectionist | Resignation due to insolvency | 9 June 1900 | William Piddington | | Protectionist |
| Sydney-Phillip | Henry Copeland | | Protectionist | Accepted post as Agent-General in London | 7 April 1900 | Daniel O'Connor | | Protectionist |
| Hastings and Macleay | Edmund Barton | | Protectionist | Resigned to take Constitution to London | 1 March 1900 | Francis Clarke | | Protectionist |
| Boorowa | Kenneth Mackay | | Protectionist | Appointed to Legislative Council | 30 September 1899 | Niels Nielsen | | Labor |
| Northumberland | Richard Stevenson | | Protectionist | Death | 20 July 1899 | John Norton | | Ind. Protectionist |
| Parramatta | William Ferris | | Independent Federalist | Election declared void by the Elections and Qualifications Committee | 26 October 1898 | William Ferris | | Protectionist |
| Hastings and Macleay | Francis Clarke | | National Federal | Resigned to give Barton a seat | 23 September 1898 | Edmund Barton | | National Federal |
| Seventeenth Legislative Assembly 1895–1898 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Sydney-Fitzroy | John McElhone | | Independent Free Trade | Death | 3 June 1898 | John Norton | | Protectionist |
| Narrabri | Charles Collins | | Free Trade | Death | 3 June 1898 | Hugh Ross | | Labor |
| Lachlan | James Carroll | | Protectionist | Resignation due to insolvency | (11 September 1896) | James Carroll | | Protectionist |
| Cowra | Denis Donnelly | | Protectionist | Death | 27 March 1896 | Michael Phillips | | Protectionist |
| Waverley | Angus Cameron | | Free Trade | Death | 18 February 1896 | Thomas Jessep | | Free Trade |
| Sydney-Phillip | Dick Meagher | | Protectionist | Resigned in disgrace in relation to the pardon of George Dean | 17 October 1895 | Henry Copeland | | Protectionist |
| Rylstone | John Fitzpatrick | | Free Trade | Election result voided by the Elections and Qualifications Committee | 14 October 1895 | John Fitzpatrick | | Free Trade |
| Sixteenth Legislative Assembly 1894–1895 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Canterbury | Varney Parkes | | Free Trade | Resignation due to insolvency | (14 June 1895) | Varney Parkes | | Free Trade |
| Bowral | William McCourt | | Free Trade | Resignation due to insolvency | (19 February 1895) | William McCourt | | Free Trade |
| Boorowa | Thomas Slattery | | Protectionist | Resigned | 15 January 1895 | Kenneth Mackay | | Protectionist |
| Willoughby | Joseph Cullen | | Free Trade | Resignation due to insolvency | 30 November 1894 | Edward Clark | | Free Trade |
| Tweed | John Willard | | Labor | Not a resident of NSW | 29 November 1894 | Joseph Kelly | | Protectionist |
| Grenfell | George Greene | | Free Trade | Election result overturned by the Elections and Qualifications Committee (no by-election) | (25 October 1894) | Michael Loughnane | | Labor |
| Fifteenth Legislative Assembly 1891–1894 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Macleay | Otho Dangar | | Protectionist | Financial difficulty | 29 May 1893 | Francis Clarke | | Protectionist |
| Central Cumberland | John Nobbs | | Free Trade | Financial difficulty | 6 May 1893 | George McCredie | | Free Trade |
| Murrumbidgee | George Dibbs | | Protectionist | Financial difficulty | (6 April 1893) | George Dibbs | | Protectionist |
| South Sydney | James Toohey | | Protectionist | Resigned | 13 February 1893 | William Manning | | Protectionist |
| East Macquarie | James Tonkin | | Free Trade | Financial difficulty | 13 August 1892 | James Tonkin | | Free Trade |
| Hawkesbury | Alexander Bowman | | Free Trade | Death | 23 July 1892 | Sydney Burdekin | | Free Trade |
| Bogan | George Cass | | Protectionist | Death | 31 May 1892 | William A'Beckett | | Free Trade |
| Bourke | Peter Howe | | Protectionist | Resigned after conviction for conspiracy to defraud | 4 December 1891 | Thomas Waddell | | Protectionist |
| Illawarra | John Nicholson | | Labor | Previous result voided by the Elections and Qualifications Committee | 3 October 1891 | John Nicholson | | Labor |
| Illawarra | Andrew Lysaght | | Protectionist | Previous result voided by the Elections and Qualifications Committee | 3 October 1891 | Archibald Campbell | | Free Trade |
| Canterbury | John Wheeler | | Free Trade | Election result overturned by the Elections and Qualifications Committee (no by-election) | (2 September 1891) | James Eve | | Free Trade |
| Central Cumberland | Robert Ritchie | | Free Trade | Death | 29 August 1891 | Jacob Garrard | | Free Trade |
| Fourteenth Legislative Assembly 1889–1891 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Wellington | David Ferguson | | Protectionist | Death | 29 May 1891 | Thomas York | | Protectionist |
| East Sydney | John Street | | Free Trade | Death | 14 April 1891 | Walter Bradley | | Protectionist |
| Newcastle | James Fletcher | | Protectionist | Death | 14 April 1891 | William Grahame | | Protectionist |
| West Macquarie | Paddy Crick | | Protectionist | Expelled for outrageous behaviour in the chamber | 6 December 1890 | Paddy Crick | | Protectionist |
| West Sydney | Alfred Lamb | | Free Trade | Death | 25 October 1890 | Adolphus Taylor | | Independent |
| Goulburn | William Teece Jr | | Free Trade | Death | 16 August 1890 | Cecil Teece | | Free Trade |
| Namoi | Tom Dangar | | Free Trade | Death | 31 July 1890 | Charles Collins | | Free Trade |
| Hartley | John Hurley | | Free Trade | Financial Difficulty | 22 July 1890 | John Hurley | | Free Trade |
| Balmain | John Hawthorne | | Free Trade | Financial Difficulty | (10 July 1890) | John Hawthorne | | Free Trade |
| Hastings and Manning | Charles Roberts | | Free Trade | Resigned | 5 April 1890 | Walter Vivian | | Free Trade |
| Monaro | Harold Stephen | | Protectionist | Death | 17 December 1889 | Gus Miller | | Protectionist |
| Newcastle | William Grahame | | Protectionist | Financial Difficulty | 12 October 1889 | James Curley | | Free Trade |
| Central Cumberland | Frank Farnell | | Free Trade | Financial difficulty | (5 October 1889) | Frank Farnell | | Free Trade |
| Central Cumberland | John Linsley | | Free Trade | Death | 22 July 1889 | David Dale | | Free Trade |
| Redfern | John Sutherland | | Protectionist | Death | 8 July 1889 | William Schey | | Protectionist |
| Tamworth | Robert Levien | | Protectionist | Sought a new mandate after being involved in a legal scandal | (18 June 1889) | Robert Levien | | Protectionist |
| Thirteenth Legislative Assembly 1887–1889 |||||||||
| By-election | Incumbent | Party | Party | Reason | Date | Winner | Party | Party |
| Gunnedah | Thomas Goodwin | | Protectionist | Resigned | 12 September 1888 | Edwin Turner | | Free Trade |
| Redfern | James Farnell | | Free Trade | Death | 8 September 1888 | Peter Howe | | Protectionist |
| Central Cumberland | Andrew McCulloch | | Free Trade | Financial difficulty | 15 May 1888 | David Buchanan | | Protectionist |
| Central Cumberland | Varney Parkes | | Free Trade | Business commitments | 14 March 1888 | John Nobbs | | Free Trade |
| Newtown | William Foster | | Free Trade | Accepted an appointment as a Judge of the Supreme Court | 25 February 1888 | Joseph Mitchell | | Free Trade |
| Newtown | Frederick Gibbes | | Free Trade | Death | 3 February 1888 | Joseph Abbott | | Free Trade |
| Paddington | William Trickett | | Free Trade | Appointed to Legislative Council | 12 January 1888 | William Allen | | Protectionist |
| Central Cumberland | Andrew McCulloch | | Free Trade | Financial difficulty | 28 December 1887 | Andrew McCulloch | | Free Trade |
| St Leonards | Henry Parkes | | Free Trade | Financial difficulty | (25 October 1887) | Henry Parkes | | Free Trade |
| Wentworth | William MacGregor | | Independent Free Trade | Resigned | 28 September 1887 | Thomas Browne | | Protectionist |
| Mudgee | Adolphus Taylor | | Free Trade | Accepted position as Examiner of Patents | 11 May 1887 | John Haynes | | Free Trade |

## No party system was discernible in the New South Wales parliament before the election of 1887

Twelfth Legislative Assembly 1885–1887 :
| By-election | Incumbent | Reason | Date | Winner |
| Bourke | Russell Barton William Sawers | Resigned | 21 January 1887 | Parliament dissolved before writ returned |
| Kiama | Harman Tarrant | Resigned | 13 January 1887 | Angus Cameron |
| New England | William Proctor | Resigned | 10 January 1887 | William Proctor |
| Yass Plains | Louis Heydon | Retired | 20 December 1886 | Thomas Colls |
| Wollombi | Lyall Scott | Retired (ill-health) | 17 December 1886 | Richard Stevenson |
| Mudgee | John Robertson | Retired (ill-health, financial difficulties and loss of premiership) | (2 July 1886) | William Wall |
| Gwydir | William Campbell | Resigned | 10 June 1886 | Thomas Hassall |
| Young | William Watson | Election result overturned by the Qualifications Committee (no by-election) | (22 December 1885) | James MacKinnon |
| Eleventh Legislative Assembly 1882–1885 |||||
| By-election | Incumbent | Reason | Date | Winner |
| Central Cumberland | John Lackey | Accepted nomination to the Legislative Council | 24 September 1885 | Varney Parkes. |
| Canterbury | Henry Moses | Accepted nomination to the Legislative Council | 16 September 1885 | William Henson |
| St Leonards | Bernhardt Holtermann | Death | 4 June 1885 | Isaac Ives |
| Argyle | John Gannon | Resigned due to ill health | 31 March 1885 | Henry Parkes |
| Carcoar | Andrew Lynch | Death | 21 November 1884 | Ezekial Baker |
| Tenterfield | Henry Parkes | Resigned, claiming that he was retiring from politics | (24 November 1884) | Charles Lee |
| Monaro | Robert Tooth | Resigned | (24 July 1884) | David Ryrie |
| West Macquarie | Thomas Hellyer | Resigned | 2 July 1884 | Lewis Lloyd |
| Northumberland | Atkinson Tighe | Resigned due to ill health | 26 May 1884 | Richard Luscombe |
| Gundagai | Bruce Smith | Resigned | 22 April 1884 | James Watson |
| Canterbury | William Pigott | Resigned (private work commitments) | 19 April 1884 | Mark Hammond |
| East Sydney | George Reid | Found to have a position of profit under the crown | 29 February 1884 | Sydney Burdekin |
| Bathurst | Francis Suttor | Found to have a position of profit under the crown | (11 February 1884) | Francis Suttor |
| Glebe | George Allen | Prolonged voyage to England. | 26 August 1883 | Michael Chapman |
| Upper Hunter | John McElhone | Challenged Adolphus Taylor to resign | 6 March 1883 | John McElhone |
| Mudgee | Adolphus Taylor | Challenged by John McElhone to resign | 6 March 1883 | Adolphus Taylor |
| East Sydney | John McElhone | Elected to two seats | 23 January 1883 | Henry Copeland |
| Newtown | Henry Copeland | Ministerial (defeated) | 13 January 1883 | Joseph Mitchell |
| Tenth Legislative Assembly 1880–1882 |||||
| By-election | Incumbent | Reason | Date | Winner |
| Gundagai | William Forster | Death | 23 November 1882 | Bruce Smith |
| Tumut | James Hoskins | Resigned to take a recuperative sea voyage | 17 October 1882 | Thomas O'Mara |
| East Macquarie | Alfred Pechey | Death | 11 July 1882 | Sydney Smith |
| Tenterfield | John Dillon | Resigned | 6 February 1882 | Augustus Fraser |
| Wentworth | William Brodribb | Appointed to the Legislative Council | 23 January 1882 | Edward Quin |
| East Macquarie | Edmund Webb | Appointed to the Legislative Council | 19 January 1882 | Alfred Pechey |
| Northumberland | William Turner | Resigned (He was supported by the local coal miners union, however the subscriptions were insufficient to support him in the assembly) | 18 January 1882 | Thomas Hungerford |
| Mudgee | Samuel Terry | Appointed to the Legislative Council | (20 January 1882) | John Robertson |
| Redfern | John Sutherland | Appointed to the Legislative Council | 11 January 1882 | Francis Wright |
| Yass Plains | Michael Fitzpatrick | Death | 10 January 1882 | Louis Heydon |
| Argyle | Phillip G. Myers | Death | 9 December 1881 | John Gannon |
| Newtown | Stephen Brown | Appointed to the Legislative Council | 1 December 1881 | Joseph Mitchell |
| Carcoar | Ezekial Baker | Expelled after he had been found to have fraudulently dealt with trust funds | 1 December 1881 | George Campbell |
| Queanbeyan | James Thompson | Resigned | 21 January 1881 | Thomas Rutledge |
| Ninth Legislative Assembly 1877–1880 |||||
| By-election | Incumbent | Reason | Date | Winner |
| Windsor | Richard Driver | Death | 29 July 1880 | Henry McQuade |
| Illawarra | Samuel Gray | Resigned | 7 July 1880 | Alexander Stuart |
| Kiama | Samuel Charles | Prolonged voyage to Europe | 2 July 1880 | Harman Tarrant |
| Northumberland | Thomas Hungerford | Resigned (attend to personal business matters) | 30 April 1880 | Ninian Melville |
| Clarence | Thomas Bawden | Resigned | 7 April 1880 | Charles Fawcett |
| Paddington | John Sutherland | Resigned (company won government contract) | 20 February 1880 | William Hezlet |
| East Sydney | Alexander Stuart | Accepted position as Agent-General in London | 17 December 1879 | Arthur Renwick |
| University of Sydney | William Windeyer | Accepted an appointment as a Judge of the Supreme Court | 26 August 1879 | Edmund Barton |
| East Macquarie | William Suttor, Jr. | Resigned | 15 August 1879 | Edward Combes |
| Mudgee 2 | Richard Rouse | Result overturned by the Qualifications Committee (no by-election) | (7 March 1879) | David Buchanan |
| Orange | Edward Combes | Found to have an office of profit under the crown | 4 March 1879 | Andrew Kerr |
| Mudgee | John Robertson | Appointed to the Legislative Council | 6 January 1879 | Richard Rouse |
| East Maitland | Stephen Scholey | Death | 5 June 1878 | Henry Badgery |
| East Macquarie | John Robertson | Elected to two seats, | 1 February 1878 | Edmund Webb |
| Eighth Legislative Assembly 1874–1877 |||||
| By-election | Incumbent | Reason | Date | Winner |
| Northumberland | Charles Stevens | Financial difficulties | 20 July 1877 | William Turner |
| Orange | Harris Nelson | Resigned | (22 February 1877) | Edward Combes |
| Williams | William Watson | Resigned | February 1877 | William Johnston |
| Mudgee | Stephen Goold | Death | 5 October 1876 | Richard Rouse |
| University of Sydney | | New seat | 8 September 1876 | William Windeyer |
| Carcoar | Solomon Meyer | Resigned due to financial difficulties | (21 June 1876) | Andrew Lynch |
| Liverpool Plains | Hanley Bennett | Financial difficulties | 5 June 1876 | Hanley Bennett |
| Hartley | Thomas Browne | Found to have held a position of profit under the crown | 21 April 1876 | John Hurley |
| Parramatta | Hugh Taylor | Resigned as he may have had a position of profit under the crown | 20 April 1876 | Hugh Taylor |
| Murrumbidgee | William Forster | Accepted the position of Agent-General in London | (6 March 1876) | Joseph Leary |
| Upper Hunter | Thomas Hungerford | By-election result voided by Qualifications Committee | 5 August 1875 | John McElhone |
| Central Cumberland | Joseph Wearne | Financial difficulties | 28 June 1875 | William Long |
| Upper Hunter | Francis White | Death | 7 June 1875 | Thomas Hungerford |
| Paterson | William Arnold | Death | 18 March 1875 | Herbert Brown |
| Seventh Legislative Assembly 1872–1874 |||||
| By-election | Incumbent | Reason | Date | Winner |
| West Maitland | Benjamin Lee | Financial difficulties | 4 August 1874 | Lewis Levy |
| East Sydney | James Neale | Resigned | 15 July 1874 | Charles Moore |
| East Macquarie | James Martin | Accepted appointment as Chief Justice | 1 December 1873 | Walter Cooper |
| Mudgee | Joseph Innes | Appointed to the Legislative Council | 8 September 1873 | Joseph O'Connor |
| Hume | James McLaurin | Resigned | 31 March 1873 | Thomas Robertson |
| Murray | Patrick Jennings | Resigned | 5 August 1872 | William Hay |
| East Sydney | Saul Samuel | Appointed to the Legislative Council | 12 June 1872 | George Oakes |
| Parramatta | Hugh Taylor | Disqualified himself at the declaration of the poll as he had a position of profit under the crown | (22 May 1872) | Hugh Taylor |
| Sixth Legislative Assembly 1869–1872 |||||
| By-election | Incumbent | Reason | Date | Winner |
| Mudgee | Henry Stephen | Resigned | 2 January 1872 | Henry Parkes |
| New England | Charles Weaver | Resigned | 28 August 1871 | Samuel Terry |
| Shoalhaven | Thomas Garrett | Accepted the position of Police Magistrate at Berrima | (28 August 1871) | James Warden |
| Liverpool Plains | Charles Cowper | Accepted the position of Agent-General in London | 9 January 1871 | Lewis Levy |
| Kiama | Henry Parkes | Financial difficulties | (12 January 1871) | John Stewart |
| Canterbury | Montagu Stephen | Prolonged visit to England | 6 January 1871 | John Lucas |
| Goldfields South | Ezekiel Baker | Accepted appointment to the Goldfields Royal Commission | 12 December 1870 | Ezekiel Baker |
| Monaro | Daniel Egan | Death | 17 November 1870 | James Hart |
| Kiama | Henry Parkes | Financial difficulties | 3 November 1870 | Henry Parkes |
| Braidwood | Michael Kelly | Result voided due to electoral irregularities | 17 October 1870 | Edward Greville |
| Hastings | Horace Dean | Election overturned as not a British subject (no by-election) | (4 July 1870) | Robert Smith |
| Wollombi | Joseph Eckford | Financial difficulties | 19 September 1870 | Joseph Eckford |
| Hastings | Horace Dean | Found to have held an office of profit under the crown | 4 July 1870 | Horace Dean |
| Goldfields South | Ezekiel Baker | Resigned | (11 July 1870) | Ezekiel Baker |
| Goldfields North | Robert Wisdom | Elected to two seats | 18 April 1870 | Robert Forster |
| West Sydney | John Robertson | Financial difficulties | 2 March 1870 | John Robertson |
| East Sydney | Henry Parkes | Elected to two seats | 23 February 1870 | Bowie Wilson |
| Fifth Legislative Assembly 1864–1869 |||||
| By-election | Incumbent | Reason | Date | Winner |
| Braidwood | Joshua Josephson | Accepted an appointment as a Judge of the District Court | (25 September 1869) | Michael Kelly |
| Goldfields West | George Thornton | Prolonged trip to England | 15 February 1869 | Walter Church |
| Central Cumberland | Allan Macpherson | Cause of resignation is unknown | 17 December 1868 | Samuel Lyons |
| West Sydney | Samuel Joseph | Prolonged trip to England | 15 December 1868 | William Campbell |
| Canterbury | James Pemell | Cause of resignation is unknown | (19 September 1868) | Richard Hill |
| Goldfields North | George Pickering | Cause of resignation is unknown | 6 July 1868 | James Hoskins |
| Upper Hunter | James White | Prolonged trip to England | 6 June 1868 | Archibald Bell |
| East Macquarie | David Buchanan | Traveled to England to study for the bar | 26 August 1867 | John Suttor |
| Orange | William Forlonge | Financial Difficulty | 1 July 1867 | George McKay |
| Central Cumberland | John Hay | Appointed to the Legislative Council | 27 June 1867 | John Lackey |
| East Sydney | Charles Cowper | Financial Difficulty | 20 March 1867 | Marshall Burdekin |
| Goldfields West | Stephen Donnelly | Cause of resignation is unknown | 26 February 1867 | George Thornton |
| Bathurst | James Kemp | Cause of resignation is unknown | (24 December 1866) | William Suttor |
| East Sydney | John Caldwell | Financial Difficulty | (24 September 1866) | Robert Stewart |
| Illawarra | Patrick Osborne | Prolonged trip to England | 6 September 1866 | John Stewart |
| Clarence | John Laycock | Cause of resignation is unknown | 27 August 1866 | John Robertson |
| Tumut | Charles Cowper Jr. | Absent from parliament without leave | 20 August 1866 | Edward Brown |
| Williams 2 | Frederick Manton | Financial Difficulty | 19 April 1866 | John Nowlan |
| Williams 1 | Marshall Burdekin | Ministerial by-election | 22 January 1866 | Frederick Manton |
| West Sydney | John Robertson | Ministerial by-election | 17 January 1866 | William Windeyer |
| Yass Plains | Peter Faucett | Accepted an appointment as a Judge of the Supreme Court | (6 November 1865) | Robert Isaacs |
| West Sydney 3 | John Robertson | Financial Difficulty | (20 October 1865) | John Robertson |
| West Sydney 2 | John Darvall | Retired to England | 7 July 1865 | Geoffrey Eagar |
| Gwydir | Tom Dangar | Position of profit under the crown | 29 June 1865 | Tom Dangar |
| Monaro | James Martin | Elected to two seats | (10 April 1865) | William Grahame |
| Canterbury | John Lucas | Elected to two seats | 24 February 1865 | James Pemell |
| Fourth Legislative Assembly 1860–1864 |||||
| By-election | Incumbent | Reason | Date | Winner |
| East Macquarie | William Suttor | Resigned | 6 October 1864 | David Buchanan |
| Kiama | Samuel Gray | Resigned | 29 April 1864 | Henry Parkes |
| Braidwood | Merion Moriarty | Death | 3 February 1864 | Henry Milford |
| Tumut | Charles Cowper, Jr. | Resigned to oppose Martin in Ministerial by-election | 16 November 1863 | James Martin |
| Orange | James Martin | Ministerial – Premier (defeated) | 4 November 1863 | Charles Cowper, Jr. |
| Clarence | Clark Irving | Absent for entire session without leave | 23 July 1863 | Clark Irving |
| East Maitland | James Dickson | Death | 18 June 1863 | John Darvall |
| Central Cumberland | James Atkinson | Resigned (Ill health) | 6 June 1863 | Allan Macpherson |
| Goldfields North | James Hoskins | Accepted position as overseer of northern roads | 7 April 1863 | James Buchanan |
| Liverpool Plains | Alexander Dick | Resigned | 29 January 1863 | Marshall Burdekin |
| West Sydney | William Windeyer | Resigned (Ill health after being shipwrecked) | 8 January 1863 | Geoffrey Eagar |
| Northumberland | Thomas Lewis | Financial difficulty | 23 December 1862 | Atkinson Tighe |
| Argyle | Terence Murray | Appointed to the Legislative Council | (30 October 1862) | Samuel Emmanuel |
| Carcoar | William Watt | Resigned | (16 October 1862) | William Dalley |
| Morpeth | David Buchanan | Financial difficulty | 18 September 1862 | Edward Close |
| Orange | John Peisley | Resigned | 28 June 1862 | James Martin |
| New England | George Markham | Resigned | 2 April 1862 | Robert Forster |
| Wellington | Silvanus Daniel | Resigned | (26 February 1862) | Saul Samuel |
| Shoalhaven | John Garrett | Resigned | (7 January 1862) | John Robertson |
| Tenterfield | Robert Meston | Resigned | 3 December 1861 | Hugh Gordon |
| Yass Plains | Henry O'Brien | Resigned (Ill health) | (15 August 1861) | Peter Faucett |
| Camden | John Douglas | Resigned to move to Queensland | (15 August 1861) | David Bell |
| Hunter | Isidore Blake | Accepted an appointment as a Judge of the District Court | 5 August 1861 | John Burns |
| Lower Hunter | Alexander Scott | Appointed to the Legislative Council | 19 July 1861 | Richard Sadleir |
| Newtown | Alexander McArthur | Appointed to the Legislative Council | 12 July 1861 | Thomas Holt |
| Patrick's Plains | William Lesley | Resigned | (4 July 1861) | Joseph Harpur |
| Goulburn | Charles Walsh | Resigned as he had achieved his aims of land and Legislative Council reform | 13 June 1861 | Maurice Alexander |
| East Sydney | Henry Parkes | Accepted position as immigration promoter in England | 29 May 1861 | William Forster |
| Upper Hunter | John Robertson | Appointed to the Legislative Council | 15 April 1861 | Thomas Dangar |
| Parramatta | James Byrnes | Resigned (unhappy that he was the second member elected for the seat) | 10 April 1861 | Arthur Holroyd |
| Third Legislative Assembly 1859–1860 |||||
| By-election | Incumbent | Reason | Date | Winner |
| Tumut | Daniel Deniehy | Elected to two seats and previous by-election voided due to voting irregularities | (1 November 1860) | Charles Cowper, Jr. |
| Braidwood | Frederick Cooper | Resigned | 10 August 1860 | Merion Moriarty |
| Morpeth | Edward Close | Resigned | 7 August 1860 | Samuel Cohen |
| Wellington | Nicolas Hyeronimus | Death | 26 July 1860 | Silvanus Daniel |
| Wollombi | William Cape | Resigned | 17 May 1860 | Joseph Eckford |
| Tumut | George Lang | Resigned (political ennui) | 10 May 1860 | Daniel Deniehy |
| East Macquarie | Thomas Hawkins | Resigned | 10 May 1860 | Daniel Deniehy |
| St Leonards | Edward Sayers | Resigned | 2 May 1860 | James Farnell |
| Hunter | Richard Jones | Resigned | (23 April 1860) | Isidore Blake |
| Liverpool Plains | Andrew Loder | Resigned after the defeat of the Foster Government | 10 April 1860 | Charles Kemp |
| Windsor | William Dalley | Prolonged visit to Europe resulting by-election | 12 March 1860 | William Walker |
| Williams | Stephen Dark | Resigned | 16 February 1860 | Alexander Campbell |
| Canterbury | Edward Flood | Resigned | 4 February 1860 | John Lucas |
| East Sydney | Charles Cowper | Was nominated and elected without his consent at previous by-election | 20 January 1860 | Peter Faucett |
| West Macquarie | John McPhillamy | Resigned | (21 December 1859) | Henry Mort |
| Mudgee | Lyttleton Bayley | Resigned after losing ministerial post | 19 December 1859 | Samuel Terry |
| East Sydney | Charles Cowper | Resigned (Ill health) | 10 November 1859 | Charles Cowper |
| Illawarra | John Hargrave | Appointed to Legislative Council | 28 October 1859 | Samuel Gordon |
| East Macquarie | William Suttor | Resigned | 6 October 1859 | Thomas Hawkins |
| Yass Plains | Thomas Laidlaw | Found to have a position of profit under the crown | (15 September 1859) | Thomas Laidlaw |
| East Maitland | Joseph Chambers | Appointed Crown Prosecutor | 15 September 1859 | James Dickson |
| Second Legislative Assembly 1858–1859 |||||
| By-election | Incumbent | Reason | Date | Winner |
| East Camden | Robert Owen | Accepted an appointment as a Judge of the District Court | 21 March 1859 | John Hargrave |
| New England and Macleay | Abram Moriarty | Resigned | (26 November 1858) | James Hart |
| Cumberland (North Riding) | Henry Parkes | Financial difficulties | (13 September 1858) | John Plunkett |
| First Legislative Assembly 1856–1858 |||||
| By-election | Incumbent | Reason | Date | Winner |
| Moreton, Wide Bay, Burnett and Maranoa | Gordon Sandeman | Resigned | (19 November 1857) | Patrick Leslie |
| Cumberland (North Riding) | John Darvall | Resigned | 11 December 1857 | Thomas Smith |
| Northumberland Boroughs | George Nichols | Death | (3 November 1857) | James Dickson |
| Cumberland (South Riding) | William Manning | Resigned | 12 June 1857 | James Byrnes |
| Argyle | John Plunkett | Appointed to the Legislative Council | (13 February 1857) | Daniel Deniehy |
| Sydney City | Henry Parkes | Financial difficulties | 29 December 1856 | William Dalley |
| Cumberland (South Riding) | Ryan Brenan | Result voided by the Elections and Qualifications Committee | (4 November 1856) | Stuart Donaldson |
| Sydney Hamlets | Stuart Donaldson | Ministerial (defeated) | 10 October 1856 | John Campbell |
| Cumberland (South Riding) | Elias Weekes | Elected for two seats | 21 August 1856 | Ryan Brenan |
| Northumberland Boroughs | Bourn Russell | Result overturned by Qualifications Committee (no by-election) | (5 August 1856) | Elias Weekes |
| Bathurst County | John Plunkett | Elected for two seats | 19 June 1856 | William Suttor |
| Western Division of Camden | James Macarthur | Believed poll to be unconstitutional | (16 June 1856) | James Macarthur |

## Causes

A by-election may occur whenever there is a vacancy in the Legislative Assembly. Vacancies can occur for reasons including:
* Death
* Voluntary resignation for any reason; historically these reasons have included:
** Retirement
** Health issues
** Family or business commitments
** Prolonged absence from the state—this occurred most commonly in the period when travel to Europe required a long sea voyage
** Loss of cabinet position, e.g., the resignation of Reba Meagher in 2008 after she lost the position of Minister for Health
** Matters of principle, e.g., Billy Dunn resigned from the seat of Mudgee in 1911 after disagreeing with his party's land ownership legislation.
** Resignation or expulsion from a political party
** To create a vacancy for a party leader who did not have a seat. This occurred most recently in 1986 when Rockdale MLA Brian Bannon resigned to enable newly elected party leader Barrie Unsworth to transfer from the Legislative Council to the Legislative Assembly.
** Public disgrace
** As a result of an inducement from an opposing party and thus create the potential for that party to increase its representation e.g. Independent MLA Alick Kay accepted an appointment to the Metropolitan Meat Board in 1927. Under a controversial use of the Legislative Assembly (Casual Vacancies) Act, he was replaced by Labor's Arthur Tonge; this gave the government of Jack Lang a secure majority in the house.
* Constitutional ineligibility to be a Member of the Legislative Assembly, including:
** Election result voided or overturned on appeal—appeals were initially made to the Qualifications Committee of the Assembly but since 1928 they have been determined by the Court of Disputed Returns
** Election to two seats—in which case the member was required to resign from one seat
** Appointment or election to the Legislative Council This occurred most commonly prior to 1936, when members of the council were appointed for life by the governor
** Election to another parliament, particularly federal parliament—members are required to resign prior to the issuing of the writs for the other parliament's election
** Having or accepting a position of profit under the crown
** Not being a citizen of Australia
** Non-residence in New South Wales for more than 6 months prior to election
** Becomes of "unsound mind"
** Insolvency
** Conviction for a major criminal offence or, since 2007, having faced trial on a charge of sexual abuse of a minor
** Absence from the house for an entire session without leave
** Expulsion from the house for infamous conduct
** Ministerial appointment Until 1904, members appointed to a ministerial position were required to face a by-election. These were generally uncontested. The political instability of New South Wales in the Nineteenth century caused a very large number of these by-elections and for convenience they have not been listed unless the minister was defeated.
It is now a convention that a by-election is not held if a vacancy occurs within 3–4 months of an expected dissolution of the parliament.