The date of the election has long been known given the fixed four-year terms of government in SA.
But Mr Rann has elected for an official four-week campaign as his Labor government seeks a third term in power.
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The Liberal Party, led by Isobel Redmond, needs to win 10 extra seats to form government.
Mr Rann committed to serving a full four-year term if re-elected at a poll he said would be "tough and tight".
"This election is critically important for our state's future, and that is what this election is about - whether or not South Australia keeps moving ahead," he said.
Voters should ask themselves which major party could continue the state's improved economic momentum, he said.
"We cannot stall the momentum that has occurred in this state and we can't risk it by handing over to people who simply aren't ready to govern," Mr Rann said.
Meanwhile, Tasmania will also go to the polls on March 20.
Labor has been in government for the past 12 years in Tasmania and is seeking a fourth consecutive term.
