India is a signer of the Chicago Convention and a founding ICAO member. As such your Indian ATP allows you to skip getting a FAA Private and Commercial certificate and go straight to the ATP level. You'll have to
(1) pass a TSA background check
(2) have the Indian DGCA verify your license to the FAA
(3) complete the ATP Certificate Training Program if you want a ME ATP
(4) pass the ATM written test for a ME ATP (there are different tests for SE and helicopter)
(5) pass a FAA medical exam
(6) pass the ATP checkride

Everything you could possibly want to know about getting a FAA certificate based on a foreign license.

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