In 2006, he played the role of Sub Inspector Solomon Joseph in Vargam. After Vargam, Prithviraj acted in Vaasthavam with the same Director, M. Padmakumar, for which he received the Kerala State Film Award for Best Actor and became the youngest actor to win the award. The same year he starred in Lal Jose's Classmates. In 2007, he starred in Chocolate, directed by Shafi. In 2008, he starred in Thalappavu, (directed by Madhupal) and Thirakkatha, (directed by Ranjith), in which he took up roles which serve as pivotal characters. One of the reviews of Thalappavu describes it as a film which is truly the coming-of-age film for Prithviraj, the actor and that there is a spartan dignity that he brings to his commanding portrayal of the Naxalite Joseph. The Sify review of Thirakkatha describes it as a "genuine attempt that keeps the viewer engaged until the end". Both Thalappavu and Thirakkatha shared the award for the best film in the Film Critics Award for 2008. He also made a special appearance in Anjali Menon's Manjadikuru.