Who is Peter Malinauskas, the new South Australian Labor leader?

Labor is well placed to return to government in South Australia in four years, new opposition leader Peter Malinauskas says.

The former union boss was on Monday endorsed as the leader of the parliamentary party, replacing Jay Weatherill after Labor's election loss last month.

Susan Close was named as his deputy and five new faces were added to the frontbench line-up as senior figures, including former attorney-general John Rau and former tourism minister Leon Bignell, stepped back.

Mr Malinauskas said it was an honour and a privilege to lead Labor as he pledged not to lead a "destructive style" opposition that sought to block every government initiative.

"Opposition is a massive challenge but this also present a great opportunity," he said.

"An opportunity for our party to reconnect. An opportunity to reset and to listen and learn, which is going to be fundamental before we can start planning a return to government."

SA LABOR PROMISES ANOTHER GIANT BATTERY IF RETURNED TO POWER

Mr Malinauskas said Labor must always commit itself to ensuring that in an increasingly prosperous society, everybody benefited.

"Equality of opportunity and an improved standard of living for everybody," he said.

"Making sure we have an economy that doesn't leave people behind.

"That is our mission. That must be Labor's core business when in government.

"But these same values should also inform the way we conduct ourselves in opposition."

The 37-year-old father of two is just Labor's third leader in the past 24 years and its sixth since the 1960s.

He entered state parliament only three years ago on a casual vacancy and joined Mr Weatherill's ministry in 2016.

He was previously the state secretary of the Shop, Distributive and Allied Employees' Association, the union that wields considerable power in Labor's dominant right faction.

Newcomers to the leader's frontbench include Lee Odenwalder, Whyalla MP Eddie Hughes, former TV journalist Jayne Stinson and Clare Scriven from Mt Gambier.

Premier Steven Marshall said he had spoken with Mr Malinauskas to congratulate him on his appointment.

But he urged the new Labor leader to support the government's agenda.

"My advice to Peter Malinauskas is very clear," he said.

"Get on board with an agenda that is going to put the people of South Australia first."