“We have won,” he told thousands of cheering supporters.
His right wing rival, ex-president Jorge Quiroga, conceded defeat.
Leftist Mr Morales, 46, highlighted that he will become the first indigenous president of South America’s poorest nation.
“The new history of Bolivia has started,” he said in his Cochabamba stronghold amid shouts of “Evo president!”
Two separate exit polls showed Mr Morales getting 51 percent of the vote, and a 20-point lead over rival Jorge Quiroga.
Before the election polls had given him about 35 percent of the vote.
“We already have 50 percent plus one,”
said Mr Morales in a reference to the
majority needed to win outright in the first round.
Even if official results show he failed to hit that mark, the leftist leader of the coca farmers movement still looks certain to become president.
If the election goes to a second round, the newly elected Congress will pick in January between the two top vote-getters.
Exit polls show Morales’ Movement Toward Socialism (MAS) party would
control enough congressional seats to defeat his rival.
Mr Morales has promised a radical shake up of the country.
The leftist lawmaker has headed popular protests that played a key role in the collapse of two governments since 2002. His campaign was marked by anti-US slogans.
On voting day, he reiterated his pledge to increase state control over Bolivia’s natural gas resources and to protect coca plantations.
Bolivia is the world’s third largest producer of coca, the base ingredient of cocaine but also a medicinal plant popular with indigenous people.
Mr Morales insists he opposes cocaine trafficking but defends the right to
grow the coca leaf. He said under his administration, “there will be zero cocaine, zero narco-trafficking but not zero coca.”
Speaking after he cast his ballot in Villa Tunari, Mr Morales said his government would cooperate closely with other “anti-imperialists,” and reiterated his admiration for Cuba’s communist President Fidel Castro.
In Venezuela, President Hugo Chavez, also a virulently anti-US leader, hailed the election, saying in a television address that Bolivia “is writing a new page in its history.”