A by-election was to be held for the New South Wales Legislative Assembly electorate of Sydney City on 4 September 1856 because of the formation of the first Cowper ministry, with Charles Cowper appointed Colonial Secretary and Robert Campbell appointed Colonial Treasurer.
| Date | Event | |
|---|---|---|
| 25 August 1856 | Formation of First Cowper ministry. | |
| 26 August 1856 | Writ of election issued by the Speaker of the Legislative Assembly.[1] | |
| 3 September 1856 | Nominations | |
| 4 September 1856 | Polling day | |
| 10 September 1856 | Return of writ |