The legendary actor stars in Varma's forthcoming film Department in which he plays a politician with a criminal past. Bachchan and Varma have collaborated on five films, also including Nishabd and Sarkar.
Speaking to Digital Spy, Varma said: "Mr Bachchan is such a versatile actor, you can literally go back and forth and you can't fault his performance.
"He's become a bad habit for me. I can't get rid of him. Every time I start sitting down to write a script immediately I think of him."
Famed for his gangster trilogy, Varma told Digital Spy that Department is not "technically" an underworld film.
"Obviously it is related to the underworld in the sense that it is focused on a department that is designed to fight crime using unusual methods that was not in line with the constitution when the gravity of the situation demanded it," he added.
"From the time of Company and Satya and all, and being involved with the police, I overheard some chance conversation which inspired me somewhere.
"Having said that, it's not really based on any true influence. It's a very commercially-based film. Very mainstream. It's presented in a new angle which the audience has not experienced before."
With over 40 films to his credit, the director offered his advice to young filmmakers and said that he remains motivated by his passion for cinema.
"There is so much technology today that filmmaking is in everyone's reach. My advice is to go out and just make the film that you want to do. Now I have even more passion for films than before."