He started his career as an actor with the television show Hip Hip Hurray on Zee TV and earned recognition through video jockeying on Channel V. He then hosted the travel show Gone India where he toured India on budget trips.
In 2010 he anchored the Zee TV music talent hunt Sa Re Ga Ma Pa Singing Superstar. He is also the host in the upcoming show Terra Quiz on National Geographic Channel.
He has also featured in television ads for Colgate, Pizza Hut, Compaq Presario, Amaron Batteries, and Castrol.
Kohli made his acting debut in films with Bus Yuhin (2003) starring opposite Nandita Das. He has also acted in other films like Supari (2003), Vastu Shastra (2004), and 13th Floor (2005). His performance in My Brother…Nikhil (2005) got him recognition. Kohli then went on to star in Mahesh Bhatt's 2006 film Woh Lamhe and as a villain again in Bhatt's 2007 film Awarapan. He also acted in Rock On!! (2008) along with Farhan Akhtar, Luke Kenny and Arjun Rampal. Kohli's work in Rock On garnered him a Special Jury Mention at the 2009 Filmfare Awards in March 2009. Kohli then starred opposite Nandita Das again in the 2010-11 film I Am which was directed by Onir, who had previously directed him in My Brother…Nikhil. He also contributed financially in the making of this film. Purab's 2014 released movie Jal is a story based on villagers fight for water and dignity.