The investment is estimated to be approximately $91.32m (A$124m).
The two patrol boats will support the Royal Australian Navy (RAN) and the Australian Border Force (ABF) in bolstering the border security in the region.
Besides, the new investment is expected to generate around 400 direct employment opportunities and around 150 jobs through Austal.
Australian Prime Minister Scott Morrison said: “This investment doesn’t just help secure our borders; it secures hundreds of shipbuilding jobs in Western Australia.
“Keeping our borders safe is a key priority for my government, and the acquisition of two more Evolved Cape Class patrol boats will boost the capability of Navy’s patrol force to ensure it is available where and when needed.”
Delivery of the two additional evolved CCPBs is expected in late 2023.
Morrison added: “More shipbuilding work means a strong economy, and a stronger future for this important industry and our Navy and Australian Border Force.”
In 2020, Austal was awarded a $257m (A$350m) contract to build six evolved CCPB for the RAN.
Under the contract, the company has already delivered the first patrol boat, Cape Otway, to the RAN in March this year.
With the acquisition of the additional vessels, the total investment into the programme increases to more than $324m (A$440m).
All the eight patrol vessels are expected to become operational by early 2024.
Australian Defence Industry Minister Melissa Price said: “This project is in addition to our planned investment of up to A$30bn in dozens of new vessels for our Navy that will be built in WA over the coming decades, supporting 2,000 WA jobs and hundreds of WA businesses in the supply chain.”