The Porsche 918 RSR racer won the EyesOn Design Award for best concept vehicle, while the Audi A6 sedan was given the award for design excellence in the category devoted to new vehicles headed for production.
The two awards were announced at the Detroit auto show, which showcases new designs from across the industry.
"Design is part of our vision. Design is in our DNA," Detlev von Platen, the head of Porsche's North America division, said.
The EyesOn Design Awards is judged annually by car designers, and has lauded Audi with four awards over the past three years.
"It's strong feedback that we have done our homework," said Achim Badstübner, head of exterior design for Audi, who accepted its award.
The other finalists for the concept award were the Ford Vertrek, a compact sport utility vehicle, and the Kia KV7 minivan, both of which were unveiled at the Detroit motor show.
The finalists for the other award were the Bentley Continental GT, the BMW 6-Series Convertible, and the Hyundai Veloster.