In the unofficial vote, an overwhelming 98% rejected President Nicolas Maduro's proposed new assembly and urged the military to defend the existing constitution.
More than seven million Venezuelans voted in Sunday's unofficial referendum held by the opposition to put pressure on President Nicolas Maduro and reject his plan to rewrite the constitution, monitors said.
The symbolic plebiscite was aimed at denting Maduro's legitimacy further amid a crippling economic crisis that has left millions struggling to eat and months of anti-government unrest that has killed nearly 100 people.
Opposition leaders hailed it as a success, while also mourning the death of one woman killed by gunmen in Caracas during the voting.
"Today, July 16, dignity won and tyranny lost," said opposition leader Maria Corina Machado.
"We have given an indisputable mandate for a new Venezuela starting tomorrow."
TRT World's Sarah Jones reports.
Maduro rejects poll
Maduro, whose term is due to end in early 2019, dismissed Sunday's opposition event as an internal exercise by the opposition with no bearing on his government.
"Don't go crazy, calm down," he said on Sunday in a message to the opposition, vowing his Constituent Assembly would bring peace to the volatile nation of 30 million people.
Voters were asked three questions at Sunday's event.
An overwhelming 98 percent of voters chose to reject the proposed new assembly, urge the military to defend the existing constitution, and support elections before Maduro's term ends in early 2019, according to academics monitoring the vote for the opposition.
Sunday's participation by nearly 7.2 million Venezuelan voters compared with 7.7 million opposition votes in the 2015 legislative elections, which they won by a landslide.
The opposition had bagged 7.3 million votes in a 2013 presidential poll which was narrowly won by Maduro.
The latest vote appeared to rejuvenate the opposition amid weariness with street protests, but does not augur for a change of government in the short term or a solution to the political stalemate.
Opposition promises "zero hour"
The opposition described the vote as an act of civil disobedience that will be followed by "zero hour," a possible reference to lengthy road blockades and sit-ins, a national strike, or possibly even a march on the Miraflores presidential palace.
"Today, Venezuela stood up with dignity to say freedom does not go backwards, democracy is not negotiated," Julio Borges, who leads the opposition-controlled legislature, said shortly after vote results were announced.
"We don't want a fraudulent Constituent Assembly imposed on us. We don't want to be Cuba. We don't want to be a country without freedom," Borges added.
Borges promised further announcements on opposition strategy during Monday.
"Maduro has done everything very badly, and now, via a fraudulent constituent assembly, he wants to gain time, but his time is up," said shopkeeper Rafael Betancourt.
Violence kills woman
The opposition coalition said a pro-government "paramilitary" gang opened fire in the poor neighbourhood of Catia in the capital.
A 61-year-old woman was killed and three people were wounded, the state prosecutor's office said.
Mariela Perez, who works in a clinic, said hundreds of people ran into a nearby church when the shots rang out. She said pro-government demonstrators then besieged those inside.
"They started yelling for the priest to come out, that they were going to set him on fire, that this plebiscite was not going to happen," said Perez, 42.
"It was horrible. We were desperate," she said. A church official eventually helped negotiate their exit.
The vote also included participation by swelling ranks of Venezuelans who have moved abroad, from Miami to Madrid, to escape the OPEC nation's dire economy.
Some public employees in Venezuela, under government pressure not to participate in opposition events, sought creative ways to vote without being noticed, such as traveling across town or even going in disguise.
The elections council, which the opposition calls a pawn of Maduro, simultaneously held a test-run on Sunday for the July 30 vote to create the constitutional assembly.
Sunday's referendum came against the backdrop of near daily anti-government protests.
Maduro has refused to recognise the authority of the National Assembly since the opposition won control of it in a 2015 landslide election, which his critics call evidence he is eroding democratic institutions in order to retain power.
He says the country is the victim of an "economic war" and that opposition protests are an effort to overthrow him with US connivance, which Washington has denied.