"We won in an open and honest fight!" a jubilant Putin, flanked by outgoing President Dmitry Medvedev, told a crowd of tens of thousands of supporters at a rally in downtown Moscow. With 30 per cent of the votes counted at 19:00 GMT, Putin was leading by a landslide, with 63.4 per cent.
"We urge everyone to unite around the interests of Russia," Putin was quoted as saying by the Russian news agency Ria Novosti. "I told you we would win and we won!" he said, his voice cracking with emotion and his eyes moist.
Russian observers and opposition leaders have alleged widespread violations in polls by supporters of Putin. An independent watchdog agency Golos said it has received reports of so-called "carousel voting," in which bus loads of voters are driven around to cast ballots multiple times, allegedly for the ruling United Russia Party candidate.
Earlier, voters turned out at 90,000 polling stations across Russia spread over 21 hours for the marathon electoral process, that is being monitored through election observers and over 100,000 webcams.
The 59-year-old ex-KGB spy will now become president for a third time after swapping role as prime minister with his close aide Dmitry Medvedev.
Putin voted in Moscow with his wife, Ludmila. His main challenger was Communist Gennady Zyuganov. The other candidates are ultra-nationalist Vladimir Zhirinovsky, tycoon Mikhail Prokhorov, who is standing as an independent, and former upper house speaker Sergey Mironov, from the centre-left A Just Russia party.
Putin was Russia's president from 2000 to 2008, but was barred by the constitution from standing for a third consecutive term. He faces four challengers, three of whom he has defeated in previous elections.