He was born on 25th of May 1972 in Mumbai. He received a Masters degree in French.

Dharma Productions, founded by his father, is Johar's production company. As a child, he was influenced by commercial Indian cinema and he cites Raj Kapoor, Yash Chopra and Sooraj R. Barjatya as his inspirations.

Johar formally entered the film industry as an actor, portraying Raj's Shahrukh Khan close friend in Dilwale Dulhania Le Jayenge. He was also assistant director on this film and helped director Aditya Chopra in writing the screenplay for this film.

Johar made his directorial debut with Kuch Kuch Hota Hai in 1998. The film won eight Filmfare Awards in 1998 including Best Movie, Best Director and all four Best Actor awards for both leading and supporting roles.

Johar's second directorial effort was the family drama, Kabhi Khushi Kabhie Gham released in 2001. His 2003 film, Kal Ho Naa Ho, was directed by Nikhil Advani.

Johar is the host of a television chat show called Koffee with Karan, in which he interviews renowned celebrities from Bollywood.