The P-8I is based on Boeing's 737 commercial airplane and is a variant of the P-8A Poseidon that Boeing is developing for the U.S. Navy.
The start of assembly work follows delivery of the plane's fuselage from Spirit AeroSystems.
Boeing workers have begun installing systems, wires and other small parts onto the fuselage. The P-8I's engines and wings will be installed this summer.
"The P-8I is a result of a close partnership between Boeing's commercial and defense units to deliver the latest and best maritime reconnaissance capability to the world," said Boeing India President Dinesh Keskar. "This agreement highlights the true commitment Boeing has toward India."
"India is our first international customer for the P-8 and we are committed to delivering this aircraft on time," said Chuck Dabundo, Boeing vice president and P-8 program manager. "The timely start of assembly and our in-line production process will allow us to meet our goal and incorporate significant efficiencies as we move forward on the program."
Boeing's contract with the Indian government, signed in 2009, calls for production of eight P-8I aircraft, with an option for four additional aircraft.