Johar entered the film industry as an assistant director on Aditya Chopra’s Dilwale Dulhania Le Jayenge (1995), which is regarded as a milestone in Hindi cinema. He then made his own directorial debut with the blockbuster romantic film Kuch Kuch Hota Hai (1998).
Karan has worked as a dress designer for Shah Rukh Khan in many films like Dilwale Dulhania Le Jayenge (1995), Dil To Pagal Hai (1997), Duplicate (1998), Mohabbatein (2000), Main Hoon Na (2004), Veer-Zaara (2004), and Om Shanti Om (2007).