The actor has refused any payment for the role of shady businessman Meyer Wolfsheim, who helps Jay Gatsby accumulate his mysterious fortune.
Bachchan wrote on his blog: "Baz Luhrmann, during his private visit to India last year, had dropped by my office to meet me and presented me with some paintings of a prominent painter that was accompanying him.
"He called last month and wondered if I would do this small role in his film and I agreed. It is a gesture. I have refused any remuneration on this too."
Bachchan, who will appear with Carey Mulligan and Leonardo DiCaprio in the adaptation, cautioned against seeing the role as a breakthrough for Indian actors.
He said: "We must remember a most basic fact. We are the Indian film industry and they Hollywood from America. There shall always be a prominence to American actors in Hollywood, just as there is a prominence of Indian actors in Indian films.
"A Shah Rukh, Salman or Aamir may well be an unknown face in one of the towns in Midwest USA, but so would a Brad Pitt or Tom Cruise in Yevatmal or Giridih."
24 star Anil Kapoor recently said that appearing in Hollywood films has given his acting career a new lease of life.