Chief of Naval Staff Adm. Nirmal Verma said the Arihant is in the last stage of testing before going to sea and within the "next 18 months" of being inducted into the navy, New Delhi TV reported.
Verma, who is to retire this month, also said he would "not get into the details" of weapons with which the submarine is scheduled to fitted.
The vessel has been built with a view to firing nuclear missiles, meaning India would then have a nuclear capability on land, air and sea, he said.
The 6,000-ton Arihant carries a crew of 100 and was built by Ship Building Center in Visakhapatnam, a port city on the southeast coast of India.
A report by the defense news Web site Defense Professionals in July 2009 said the Arihant design possibly is based on the older 5,000-ton Russian Charlie-II class submarine. Russia decommissioned its last Charlie class sub in 1994.
The Arihant will join the 8,000-ton Chakra, the former Russian nuclear submarine Nerpa, an Akula II class vessel which India took control of in January.
The Akula II class Nerpa submarine will be with the Indian navy under a 10-year lease from the Russians, a Times of India report said in January.
Handover of the Nerpa was completed at the Russian Bolshoi Kamen shipbuilding yard in Bolshoy Kamen, a small coastal town 25 miles from Vladivostok and whose main activity is construction and repair of nuclear subs.
The Nerpa left Russia after a controversial history, including a fatal on-board fire in November 2008 just after the vessel was made operational by the Russian navy.
Verma said commissioning of the Chakra in January launched India into a "select group of six nations" and has added "considerable punch to our maritime power."
Nuclear submarines are operated also by the United States, Russia, Britain, France and China.
India briefly operated a nuclear submarine form 1988-91 when it leased a Charlie class vessel from Russia. It, too, was called the Chakra while in service with the Indian navy.
The Chakra and Arihant come at a time of "declining" capability for the navy's Russian Kilo and German HDW diesel-electric submarines which are spending increasing time in harbor for servicing and refits.
Verma said for this reason the navy is pushing the Defense Ministry to procure the building of at least two more submarines at Indian shipyards.