List of New South Wales state by-elections

• Brackets around a date 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 ; for the Liberal Party and its predecessors in ; for the National Party and its predecessors in ; for independents and minor parties in ; for the Free Trade Party in and for the Protectionist Party in.

Fifty-eighth Legislative Assembly 2023–2027

Fifty-seventh Legislative Assembly 2019–2023

Fifty-sixth Legislative Assembly 2015–2019

Fifty-fifth Legislative Assembly 2011–2015

Fifty-fourth Legislative Assembly 2007–2011

Fifty-third Legislative Assembly 2003–2007

Fifty-second Legislative Assembly 1999–2003

Fifty-first Legislative Assembly 1995–1999

Fiftieth Legislative Assembly 1991–1995

Forty-ninth Legislative Assembly 1988–1991

• 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

Forty-seventh Legislative Assembly 1981–1984

Forty-sixth Legislative Assembly 1978–1981

Forty-fifth Legislative Assembly 1976–1978

Forty-fourth Legislative Assembly 1973–1976

Forty-third Legislative Assembly 1971–1973

Forty-second Legislative Assembly 1968–1971

Forty-first Legislative Assembly 1965–1968

Fortieth Legislative Assembly 1962–1965

Thirty-ninth Legislative Assembly 1959–1962

Thirty-eighth Legislative Assembly 1956–1959

Thirty-seventh Legislative Assembly 1953–1956

Thirty-sixth Legislative Assembly 1950–1953

Thirty-fifth Legislative Assembly 1947–1950

Thirty-fourth Legislative Assembly 1944–1947

Thirty-third Legislative Assembly 1941–1944

Thirty-second Legislative Assembly 1938–1941

Thirty-first Legislative Assembly 1935–1938

Thirtieth Legislative Assembly 1932–1935

Twenty-ninth Legislative Assembly 1930–1932

Twenty-eighth Legislative Assembly 1927–1930

Twenty-seventh Legislative Assembly 1925–1927

Twenty-sixth Legislative Assembly 1922–1925

Twenty-fifth Legislative Assembly 1920–1922

Twenty-fourth Legislative Assembly 1917–1920

Twenty-third Legislative Assembly 1913–1917

Twenty-second Legislative Assembly 1910–1913

Twenty-first Legislative Assembly 1907–1910

Twentieth Legislative Assembly 1904–1907

Nineteenth Legislative Assembly 1901–1904

Eighteenth Legislative Assembly 1898–1901

Seventeenth Legislative Assembly 1895–1898

Sixteenth Legislative Assembly 1894–1895

Fifteenth Legislative Assembly 1891–1894

Fourteenth Legislative Assembly 1889–1891

Thirteenth Legislative Assembly 1887–1889

Twelfth Legislative Assembly 1885–1887

Eleventh Legislative Assembly 1882–1885

Tenth Legislative Assembly 1880–1882

Ninth Legislative Assembly 1877–1880

Eighth Legislative Assembly 1874–1877

Seventh Legislative Assembly 1872–1874

Sixth Legislative Assembly 1869–1872

Fifth Legislative Assembly 1864–1869

Fourth Legislative Assembly 1860–1864

Third Legislative Assembly 1859–1860

Second Legislative Assembly 1858–1859

First Legislative Assembly 1856–1858

Causes

• * 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 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.