The Volkswagen unit is set to own 24% of the Croatian firm.
It's the second time it's raised its stake since an initial investment in 2018.
The new deal values Rimac at 947 million dollars.
Porsche says the firm is becoming a strong player in building prototypes and limited-number production cars.
It says Rimac is well on its way to becoming a tier-1 supplier for the high-tech segment.
Since Porsche's first investment, Rimac has nearly doubled its workforce, and collaborated with carmakers including Hyundai, Kia and Aston Martin.
Company founder and boss Mate Rimac says it's a privilege to have Porsche as a shareholder.
