A by-election was held for the New South Wales Legislative Assembly electorate of West Sydney on 17 January 1866 because John Robertson had been re-appointed Secretary for Lands in the fourth Cowper ministry.[1] Such ministerial by-elections were usually uncontested however on this occasion a poll was required at both West Sydney and The Williams (Marshall Burdekin). Both Robertson and Burdekin were defeated, with the Cowper government falling, replaced by the second Martin ministry.
| Date | Event | |
|---|---|---|
| 1 January 1866 | John Robertson re-appointed Secretary for Lands.[2] | |
| 9 January 1866 | Writ of election issued by the Speaker of the Legislative Assembly.[3] | |
| 15 January 1866 | Nominations | |
| 17 January 1866 | Polling day | |
| 20 January 1866 | Return of writ |