The director took to Twitter to make the announcement on the occasion of Shastri's 113th birth anniversary today.
"On this day when India's most honest, successful and loved leader, Shri Lal Bahadur Shashtri was born, we begin the pre-production and casting of our film on his mysterious death in Tashkent," wrote Agnihotri.
The filmmaker also shared a poster with Shastri's picture and the tentative title of the film is "Bharat Ke Lal".
Agnihotri had announced in January that his next project will be dedicated to the statesman.
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"Death/assassination, questions must be answered. Contribute ideas. This will be first crowdsourcing of ideas for a film."
Agnihotri had also shared a poster, which read, "I think it is our democratic right to know if our second Prime Minister Shri Lal Bahadur Shastriji died a natural death, or, as alleged, was it an assassination? Why the cover-up?"
Shastri passed away on January 11, 1966 in Uzbekistan, after signing the Tashkent Declaration with Pakistan.
He reportedly died due to cardiac arrest at the age of 61.