Narayanan, who was in-charge of overall ISRO's cryogenic project and had introduced the liquid fuel rocket technology in India in early 1970s, was falsely charged in a 1994 espionage case.
In a judicial relief that came after an 18-year-long wait, the Kerala High Court earlier this month directed payment of Rs 10 lakh as compensation to him, upholding the 2001 NHRC decision which the state government had challenged.
"The ISRO story is both shocking and moving - a great human account as well as a sensational mirror to our nation on self-destruct. Nambi Narayan is an example of a brilliant mind reduced to shambles. This film will be truly international and global cinema," Mahadevan says about "The Witch Hunt", which will be in Hindi and Malayalam.
Mahadevan feels Mohanlal is one of India's best actors.
"For a film like this, which explores a space and character that Indian cinema hasn't so far, it had to be an actor who rose above all other trappings, an actor who became the character with effortless ease," Mahadevan told PTI.
Narayan was initially wary about the project.
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"But after watching my films and hearing me out as to how the film would be pitched, he is overwhelmed. It's an honour to document a brilliant life and mind for me and his offer to be consultant on the project has further charged me up."
The rest of the cast will be from Hindi cinema. Several other big names will be involved in the film.
"Celebrated writer C P Surendran, Oscar-winning sound designer Resul Pookutty, eight times National award winning editor Sreekar Prasad and maestro L Subramaniam on the music will further enhance the film," Mahadevan says.
His Marathi biopic "Mee Sindhutai Sapkal" was crtically acclaimed and did very well in the festival circuit.
His next film "Gour Hari Daastaan" is also a biopic on freedom fighter Gour Hari Das, with Vinay Pathak in the lead.