A by-election for the seat of Dunstan in the South Australian House of Assembly was held on 23 March 2024, following the resignation of incumbent member and former premier Steven Marshall, which was announced on 24 January 2024.
Labor candidate Cressida O'Hanlon, who challenged Narshall for the seat two years earlier, was elected the new member, defeating Liberal candidate Anna Finizio. O'Hanlon is the first Labor member to represent the seat in its present incarnation; it was created in 2014 as a reconfiguration of Norwood, the seat of former Labor premier Don Dunstan. She is only the second member other than Marshall to have represented the seat since then. It is the first instance of a governing party gaining a seat in a by-election from the Opposition in South Australia in over a century.
The by-election was triggered by the resignation of sitting Liberal MP and former premier Steven Marshall.
Dunstan is considered an ultra-marginal seat, sitting on a 0.5% margin. Indeed, at the 2022 state election, when Marshall's Liberal government unsuccessfully sought a second term (but were defeated in a landslide), Marshall suffered a nearly seven percent swing, and O'Hanlon narrowly missed taking the seat off the Liberals. When all preferences were distributed, Marshall came within 260 votes of losing his own seat.
List of candidates as they appear on the ballot order.