Labor is set to replace former premier Jay Weatherill with its ex-health minister Peter Malinauskas as the new South Australian opposition leader.

Mr Malinauskas moved from the Upper House to the House of Assembly at last weekend's election, taking over the safe Labor seat of Croydon.

He has long been touted as a likely future ALP leader.

"After much reflection and discussion with my family, I have decided to nominate for the position of leader of the South Australian parliamentary Labor Party," Mr Malinauskas said in a statement.

"I will spend the coming days having discussions with my parliamentary colleagues."

The expected path to the leadership has been cleared for the former shop workers' union official by a withdrawal of the right faction's other prospect, former treasurer Tom Koutsantonis.

Both MPs are close friends.

Mr Malinauskas's deputy is likely to be former education minister Susan Close, from Labor's left faction.

"Despite the obvious disappointment of losing government, the future for our party and movement is bright," Mr Malinauskas said.

The ALP caucus will meet to formalise the appointments on April 9.

Mr Weatherill announced the day after his election defeat he would move to the backbench for the next four years and planned to focus on being a good local MP and spend more time with his family.

Steven Marshall was installed as SA's new Premier last Monday, and Vickie Chapman as his deputy.