Two OPVs are being built at the Osborne shipyards, with a further 10 to be constructed in Western Australia as part of a $4 billion program.
Premier Steven Marshall says putting the new ship in the water is a further boost to SA's credentials as Australia's defence capital.
"Today is a significant milestone for the OPV program and an important step in Australia's continuous naval shipbuilding program," he said.
"South Australia has well and truly cemented its position as the defence and space capital of the country and will continue to power forward and play its part in building and sustaining the nation's sovereign capabilities.
"Work on these projects will deliver thousands of jobs in the decades to come, ensuring current and future talent can forge lifelong careers in naval shipbuilding, right here in South Australia."
The OPV program is part of a major expansion of the nation's naval capabilities with further work in SA to include a fleet of nine Hunter Class frigates, up to eight nuclear-powered submarines, full-cycle docking for the Collins Class submarines and a major upgrade of the Hobart Class destroyers' combat management system.
Mr Marshall said the continuous pipeline of projects was a once-in-a-generation opportunity to create a sustainable supplier base for Australia and develop the skilled and technical workforce required to deliver complex defence projects.
The Arafura OPVs will be used mainly for border patrol and have a crew of 40.
The 80-metre diesel-powered vessels have a displacement of 1640 tonnes, a top speed of 20 knots and a range of more than 7000 kilometres.