"This development means that the electricity supply process has started," The Wall Street Journal quoted an unidentified executive of state-run Nuclear Power Corporation of India Ltd. as saying Tuesday.
Environmentalists, anti-nuclear campaigners and local residents have protested the Kudankulam plant since 1988 over concerns radiation from the plant could endanger those who live in close proximity to it. Opposition to the facility intensified after Japan's Fukushima nuclear plant disaster in March 2011.
Construction on Kudankulam began in 2002 but wasn't completed until 11 years later because of delays caused by the anti-nuclear protests.
India's Supreme Court in May dismissed petitions challenging the 1,000-megawatt first unit of the facility.
The reactor is the first as many as six India-Russia-designed units planned for the Kudankulam complex.
Kudankulam's second 1,000-megawatt unit would likely be commissioned by June 2014, Nuclear Power Corporation told the Journal.
"The Kudankulam nuclear power project is an important symbol of our strategic partnership," Prime Minister Manmohan Singh said in a statement after talks with Russian President Vladimir Putin in Moscow Monday. "We look forward to commercial power production from Unit 1 very shortly, and the completion of work on Unit 2 next year."
During Singh's visit to Moscow, Indian and Russian officials discussed the proposed third and fourth units of the Kudankulam plant.
The two countries did not sign a deal as had been expected because of Russia's concerns about an Indian law that fixes compensation liability on an equipment supplier in the event of an accident.
In most countries only the operator of the facility is liable.
"We have directed our officials to resolve all outstanding issues at the earliest," the Indian prime minister said, the Hindustan Times reports. He said he gave Putin his commitment "to fully implement the road map on civil nuclear cooperation."
Prior to the commissioning of Kudankulam, India had 20 operational nuclear reactors in six nuclear power plants with a capacity of 4.4 gigawatts, generating less than 3 percent of the country's total electricity. Ten of those reactors were commissioned after 2000, the last in January 2011.
The government aims to increase total nuclear capacity to 35 gigawatts by 2020.
India has 211 gigawatts of installed electricity capacity, mostly in coal-powered plants. Because of insufficient fuel supply, the country suffers from a severe shortage of electricity generation, leading to rolling blackouts.