The federal by-election for the Sydney seat of Wentworth has been announced for the 20th of October.
The New South Wales seat was previously held by Malcolm Turnbull, who vacated it when he resigned from parliament.
Polling has revealed the Liberal vote has fallen dramatically since Mr Turnbull resigned.
Speaker Tony Smith says electoral rolls will close on the 24th of September, while candidate nominations are due by the 27th of September.