The aircraft, built under a 2009 contract, arrived in India Wednesday.
"Boeing is proud to deliver this advanced aircraft to meet the Indian navy's unique maritime patrol requirements," said Boeing Military Aircraft President Chris Chadwick.
"The P-8I team, which includes our customer and Indian suppliers, has done a fantastic job working together and we're on track to deliver the next two P-8I aircraft later this year."
The P-8I is a variant of the P-8A being developed for the U.S. Navy. It has unique features requested by India as well as Indian-built subsystems tailored to the country's maritime patrol requirements.
The P-8 Poseidon is based on Boeing's 737-800 commercial aircraft. It has a maximum speed of 490 knots per hour and a range of 1,200 nautical miles.