Mr Lucas will retire at the next election in March, bringing a stellar political career to a close.

The 68-year-old was first elected to the state's upper house in 1982 and previously served as treasurer from 1998 to 2002.

He returned to the role when the Liberals won the 2018 election but quite quickly announced it would be his last term in the parliament.

On Tuesday, Mr Lucas handed down a budget which forecasts a $1.39 billion deficit on the back of extra spending to overcome the impact of the COVID-19 pandemic.

But the budget also points to a return to surplus the following year, one year ahead of original predictions.

Mr Lucas said he believed South Australia was now on the dawn of a very exciting future with promised defence spending, the growth of the space industry and the development of the hydrogen sector set to boost jobs and the state's economic outlook for years to come.

"I'm normally a pretty miserable person, pessimistic at the best," he said.

"But I leave you with my final note, that I'm as excited about our state's future as I've ever been.

"I look forward to watching, as I sail off into the political sunset in March next year, what I hope are future exciting developments from the foundations that this budget and other budgets have put in place."

As to his successor, the treasurer said it was not his place to nominate an individual or for the government to presume it would win the next election.

But he said there were already five or six people in the cabinet already well versed with the budget process.

Australian Associated Press