Embattled state Liberal leader quits after party unrest

"This has not been an easy decision, however I believe it is in my best interests and that of my family," he said in a statement on Thursday.

"I have used the mid-winter break to reflect on my priorities and to speak with family and friends at length about my future. Ultimately, I want to spend more quality time with them and the demands of the role as leader makes this difficult."

David Speirs said he was proud of his achievements as leader during two years in opposition. (Roy Vandervegt/AAP PHOTOS)

Speculation over his future as leader has mounted in recent weeks, and in July he dared any plotters to "come on and challenge me".

Mr Speirs said he was proud of his achievements while spearheading a rebuild of the party following Labor's landslide victory at the 2022 state election.

The Liberals have served just one term in office in SA in the past two decades - under former premier Steven Marshall - with Labor otherwise reigning supreme.

The Advertiser reported that deputy leader John Gardner was positioned as the likely replacement.

The party was believed to be trying to avoid a ballot to install Mr Gardner, a senior figure in the party's moderate faction.

Mr Speirs said it had been "an absolute privilege and honour" to lead the party.

"I have given it my all and I look forward to continuing to serve the people in my electorate of Black, in the southern suburbs," he said.

"South Australians are doing it tough right now and they deserve a better state government that will put them first."

Mr Speirs became the party leader in April 2022, replacing Mr Marshall after Peter Malinauskas led Labor to a landslide victory.

"To be able to go from an overseas migrant who settled in the southern suburbs of Adelaide as a teenager, to become the leader of the South Australian Liberal Party, is something I am immensely proud of, and highlights the incredible opportunities available to all South Australians in this remarkable state," Mr Speirs said.