A by-election was held for the New South Wales Legislative Assembly electorate of West Sydney on 15 July 1877 because Sir John Robertson was appointed Colonial Secretary, forming the fourth Robertson ministry. Such ministerial by-elections were usually uncontested however on this occasion a poll was required in Central Cumberland (John Lackey and William Long), East Sydney (John Davies), Orange (Edward Combes) and West Sydney. Each minister was comfortably re-elected. Only Camden (Thomas Garrett) and Goldfields South (Ezekiel Baker) were uncontested.
|17 August 1877||Fourth Robertson ministry appointed.|
|18 August 1877||Writ of election issued by the Speaker of the Legislative Assembly.|
|24 August 1877||Nominations|
|27 August 1877||Polling day|
|17 September 1877||Return of writ|
- Sir John Robertson had been a member for West Sydney since 1869, having previously represented the district from 1864 to 1866. This was the final occasion on which he was elected for the district, being defeated two months later at the 1877 election, but was then elected to both East Macquarie and Mudgee.
- Thomas White was the president of the Seamen's Union and a former secretary of the Trades and Labor Council. This was his first time standing for election to the Legislative Assembly and he would also stand unsuccessfully for West Sydney at the 1877, and 1880 elections.
|Sir John Robertson (re-elected)||1,703||54.6|
|Total formal votes||3,117||97.0|
- estimate based on an electoral roll of 10,097 at October 1877.
- "Sir John Robertson (1816–1891)". Former Members of the Parliament of New South Wales. Retrieved 18 April 2019.
- Green, Antony. "1875 to 1877 by-elections". New South Wales Election Results 1856-2007. Parliament of New South Wales. Retrieved 8 September 2020.
- "Appointment of ministers". New South Wales Government Gazette. No. 266. New South Wales, Australia. 14 May 1872. p. 3195. Retrieved 7 September 2020 – via Trove.
- "Writ of election: West Sydney". New South Wales Government Gazette. No. 267. 18 August 1877. p. 3197. Retrieved 7 November 2020 – via Trove.
- Green, Antony. "1877 West Sydney". New South Wales Election Results 1856-2007. Parliament of New South Wales. Retrieved 7 November 2020.
- Green, Antony. "1880 West Sydney". New South Wales Election Results 1856-2007. Parliament of New South Wales. Retrieved 7 November 2020.
- Green, Antony. "1877 West Sydney by-election". New South Wales Election Results 1856-2007. Parliament of New South Wales. Retrieved 7 November 2020.