The government announced that, with 90 percent of the votes tallied, the socialist, who has long been a foe of Washington, received 54 percent to Capriles' 45 percent.
"Thank you, my God. Thanks to everyone. Thanks, my beloved people!!! Viva Venezuela!!!! Viva Bolivar!!!!!" Chavez said in a Twitter message.
Simon Bolivar was a 19th century Venezuelan military and political leader who played a key role in Hispanic America's successful struggle for independence from the Spanish empire.
Venezuelan voter turnout Sunday was nearly 81 percent, the highest in decades, National Electoral Council President Tibisay Lucena announced on national television. The government reported nearly 19 million registered voters.
Fireworks erupted in the capital Caracas after the announcement, and Chavez supporters celebrated in the streets.
Shortly before 11:30 p.m. local time (midnight EDT), Chavez, who has been president since 1999, stepped out onto the balcony of the presidential Miraflores Palace. He waved at supporters and said, "My words of recognition go out from here to all who voted against us, a recognition for their democratic temperament," The New York Times reported.
Chavez, 58, a former soldier, called the election a "perfect battle."
Before the results were announced, he told reporters by phone: "Tomorrow, we are only one country, only one Venezuela. Tomorrow in the country there are many problems that we have to resolve. Problems do not wait."
Capriles, 40, a lawyer-turned-politician, told grim supporters he congratulated Chavez and said he hoped the president would see the result as "the expression today of a country with two visions, and to be president means working to solve the problems of all Venezuelans."
He appeared downcast, several news organizations reported, but said he was proud of the large number of voters who turned out to cast their ballots for him.
"You should all feel proud -- do not feel defeated," he said.
Capriles, governor of Venezuela's No. 2 state of Miranda, which includes part the metropolitan Caracas, had never lost an election.
He appeared ready to continue his fight in the elections for state governors in December, the Times said.