The latest injection is Porsche's third into the nascent Croatian manufacturer, following an initial acquisition of a 10% stake in 2018, before boosting that by more than half the following year.
Since that first investment, Rimac has doubled its workforce to nearly 1000 people and readied its 1888bhp C_Two electric hypercar for production this year.
In addition to Porsche, Rimac now has technical and strategic partnerships in place with Hyundai, Kia, Aston Martin, Automobili Pininfarina, Koenigsegg and others.
Founder and CEO Mate Rimac said: "Porsche has been a big supporter of our company since 2018 and it has always been a privilege to have one of the world's most iconic sports car brands be a part of Rimac.
"We're proud to work together on new exciting and electrified products and of the fact that Porsche's trust in Rimac resulted in several rounds of investment, making Porsche an important shareholder of the company."
Despite the increased backing from the German sports car maker, Rimac said his firm will "remain an entirely independent business" and its projects and shareholders will always be kept "entirely separate".
Porsche said it has already placed orders with Rimac for "the development of highly innovative series components" and the two firms will expand upon their existing collaborative relationship.