Thousands of voters in one of Adelaide's most marginal seats will return to the polls next month for the Dunstan by-election, following former premier Steven Marshall's resignation.
Speaker Dan Cregan confirmed on Thursday afternoon the by-election will be held on Saturday, March 23.
Mr Marshall flagged his intention late last month to quit politics, and on Tuesday said he had formally tendered his resignation as the member for Dunstan.
According to the Electoral Commission of South Australia, there are more than 27,000 electors enrolled to vote in the inner suburban electorate.
It is the second by-election to be held in South Australia since the Liberal government was defeated after just one term at the March 2022 election.
Former deputy premier Vickie Chapman triggered a by-election in the seat of Bragg in Adelaide's east, which was retained by the Liberals.
Mr Marshall retained Dunstan at the 2022 election, with the Liberals holding it by 0.5 per cent.
Labor's Cressida O'Hanlon will re-contest the seat for Labor, with the Liberals formally pre-selecting lawyer, former Liberal staffer and factional moderate Anna Finizio, while Katie McCusker will contest for the Greens.
Mr Marshall first entered South Australia's parliament in 2010 and became Liberal leader in 2013.
He served as premier for four years, including during the height of the COVID-19 pandemic.
While he was reluctant to examine the reasons for the 2022 defeat, saying he instead wanted to "leave the commentary to the commentators", Mr Marshall attributed the result partly to the pandemic.
"Certainly, Omicron was not a particularly helpful occurrence just before the election when we did have to put some restrictions in place," he said.
"There have been some moments which didn't go exactly the way I would like [them] to have gone, but I certainly don't leave with any animosity in my heart.
"COVID, bushfires, drought, fruit fly, I mean it was a pretty difficult period."