Sircar previously made Johnny Mastana starring Amitabh three years ago, but it is currently unreleased.
Speaking to The Times of India, the director said: "[The new film is] a retrospection of a marriage in the closing years of a couple's life when they're certain that one of them would go before the other.
"After spending 35 years together, how does one half of the marital pair prepare to face a spouseless existence?"
Describing it as an intensely romantic film about an aged couple, he said: "True love doesn't diminish over the years. It just turns into a different shade of emotion than what it was earlier. I want to explore the unconditional love of a couple who have devoted their lives to one another."
With the script ready, Sircar has been regularly visiting the Bachchan residence to finalise the project.
"Mr Bachchan and I spent two years of our lives working on Johnny Mastana. It's unfortunate that the film is still unreleased. I still say it's one of Mr Bachchan's best works to date. My next film with him would be even better," he said.
The couple last starred on screen together in Kabhi Khushi Kabhie Gham... in 2001.
A sequel to that film has been discussed.