Marshall, who was Liberal Premier from 2018 to 2022, announced this morning that the first sitting day of state parliament for 2024 would be his last as an MP.

Marshall first revealed on January 24 that he would not see out his term as Dunstan MP, but refused to give a date for his resignation, only signalling that it would be at the “halfway point” of the four-year election cycle – likely March.

But in a lengthy LinkedIn post early Tuesday, Marshall said: “Today is my last day in the South Australian Parliament – time for new challenges.”

He then listed a series of his government’s achievements, noting that his term was “naturally marked by the Covid pandemic”.

Opposition leader David Speirs has said the Liberal Party will be the “underdog” in the fight for Dunstan, which Marshall held onto at the 2022 state election with a margin of just 0.5 per cent.

His Labor opponent was Cressida O’Hanlon, who will again be the party’s candidate for the by-election, the timing of which will be determined by the SA Electoral Commission and the Speaker of the House of Assembly, independent Dan Cregan.

Asked on January 24 why he was not giving his date for his resignation, Marshall said: “By announcing it today that I will be resigning in the coming months… it gives the party the chance to preselect the very best candidate to give ourselves the best shot for the by-election.”

“The by-election will be a referendum at the halfway point of the Malinauskas government – they got elected on a single promise to fix ramping, by any measure they haven’t done that.”

The Liberal Party then announced that its candidate for Dunstan would be moderate-aligned former ministerial adviser Anna Finizio.

Finizio wrote an InDaily column in 2023 in which she criticised a focus by some in the Liberal Party on “niche culture war issues”, and said that women voters were being let down by policies from both major parties.

The Liberal Party currently only has two women – Ashton Hurn and Penny Pratt – in the Lower House compared to 13 men.