Marshall, who led the state from 2018 to 2022, is expected to announce his intention to retire in the coming months at a press conference in Norwood this morning alongside Opposition leader David Speirs.

The resignation announcement comes nearly two years since 2022 state election, which saw the toppling of the one-term Marshall Government and the former premier clinging onto Dunstan on a paper-thin majority of 0.5 per cent.

Marshall entered state parliament as the MP for the then seat of Norwood – now known as Dunstan – at the 2010 state election, ending former Labor MP Vini Ciccarello’s 13-year reign and marking the first time that Labor had been in government without holding the eastern suburbs seat.

He was promoted to the Liberals’ frontbench one year later, before succeeding Isobel Redmond as leader in 2013.

Marshall led the Liberals to victory at the 2018 election, ending Labor’s record 16-year reign and shrugging off a challenge from Nick Xenophon’s fledgling SA Best Party.

But after a four-year term – the second half of which was marred by the COVID-19 pandemic and an allowances scandal that saw his government lose its majority in the Lower House – the Liberals suffered a landslide defeat at the 2022 election.

The former premier himself was at risk of losing his seat, suffering a swing of almost 7 per cent and leaving Dunstan the most marginal seat in the chamber.

Marshall’s decision to retire from politics will trigger a by-election in Dunstan.

Labor’s candidate for Dunstan at the 2022 election, businesswoman Cressida O’Hanlon, indicated to InDaily last year she intended to put her hand up to run again.

Meanwhile, former government staffer and lawyer Anna Finizio has been widely touted as the frontrunner for Liberal pre-selection.

The Greens are also bullish about their prospects in Dunstan, after recording a 5 per cent swing in the seat at the last election.

–InDaily staff writers