The 34-year-old former model will be pitched opposite Hollywood superstar Rachel Weisz, who has starred in some popular films like "Constant Gardner", "Constantine" and "Mummy".
"John, who plays an environmentalist in 'Luna', is not an Indian, nor an American in the film. His culture origins aren't specified," Mehta told.
"Unlike 'Water' he won't play a man in a dhoti playing the flute in 'Luna'. This makes him Bollywood's first actor to crack the West without playing an NRI or some exotic creature. He has a full-fledged role opposite Rachel," he added.
Two-time Oscar-winner David Ward will write the script for "Luna".