Governor Frances Adamson issued the election writs on Saturday, kickstarting the four-week countdown to the March 19 poll.
The election is expected to be close and be dominated by the impacts of COVID-19.
Mr Marshall said it was clear that South Australia had done well in the face of the global pandemic, growing the economy and keeping people in jobs.
"The risk to this is a change in government," he said.
"This election, more than any before, is an election on trust. Who do you trust to keep building a stronger South Australia?"
But Mr Malinauskas said the government was tired and divided, and had the wrong priorities.
"South Australians have a clear choice for their future," he said.
"At this election, we are presented with an opportunity not seen since the end of World War II.
"This is our chance to ensure the legacy of the pandemic isn't just a bad memory."
Jobs and health care are set to be key issues for voters but less clear is what impact the government's handling of the pandemic will have.
It did well in the early stages as it steadfastly followed health advice but drew criticism after opening the state's borders in November which brought a surge in virus infections.
That wave has subsided but not before having a significant effect on local businesses that were hit with new restrictions over the usually busy Christmas-New Year trading period.
Special arrangements have been put in place for next month's poll to ensure voters can cast their ballots safely and to allow those who could be in isolation with the virus on election day to vote.
Electoral Commissioner Mick Sherry urged voters to ensure their details were correct with the electoral roll closing in less than a week.
"If you have moved house, become a citizen, or turned 18 since the last election, use this weekend to check your details or register to vote," he said.
"It is our hope that every eligible South Australian has enrolled to ensure they have the opportunity to vote on the issues that are important to them in this election."
Candidate nominations open on Monday, while the last day for voters to enrol is February 25.
Early voting will start on March 7.
The electoral commission is expecting a significant rise in postal and pre-poll votes, partly due to issues surrounding COVID-19.
The Liberal government currently holds 22 seats in the 47-seat House of Assembly to Labor's 19.
The remaining six are held by independents, although three of those were originally voted in as Liberals before leaving the party.
How those independents fare and who they potentially support to form a government could be crucial to the result.
