It was a moment that Maduro opponents hoped to derail -- they boycotted Sunday's election and demonstrated against it for weeks, saying the President orchestrated it to get around the existing National Assembly, which the opposition has controlled since 2015.
But the new assembly's leader, former Foreign Minister Delcy Rodriguez, warned the opposition that their reckoning is coming, blaming it for deaths that accompanied the protests and for waging "economic war" against the people.
"For those who preach violence, to the fascists, to those who wage an economic war against people ... justice will come to them," Rodriguez told the new assembly inside the legislative palace in Caracas. "We shall start to act as of tomorrow. Do not be surprised."
One of Maduro's top officials has previously said the new body will establish a "truth commission"
to prosecute those accused of having broken laws ahead of the election.
Virtually all of the National Constituent Assembly members are Maduro supporters, and the new assembly could abolish the old one as well as other state institutions.
Rodriguez also took aim at countries like the United States, which issued sanctions over the election.
"To the head of the empire, we said: Don't mess with Venezuela," she said to fierce applause. "We say, empire, savage barbarians, don't mess with Venezuela, because Venezuela will never surrender."
Critics say the new assembly could erase any last traces of democracy in the South American country. It comes to power amid allegations that turnout figures in Sunday's election were inflated
Its installation also follows months of sometimes deadly anti-regime protests and an economic crisis
that led many to leave Venezuela
in search of easier access to food and medicine.
There were some protests Friday in Caracas. A CNN crew saw national police shoot tear gas and rubber bullets at demonstrators.
Thousands of Maduro supporters, most wearing red shirts, walked in a separate march.
Hundreds of Maduro supporters, some carrying Venezuelan flags and other banners, marched to the legislative palace in support of the new assembly.
When the new assembly members entered the legislative palace, some carried portraits of independence hero Simon Bolivar and the late President Hugo Chavez, the socialist leader who handpicked Maduro as his successor before his death in 2013.
The portraits of Bolivar and Chavez in the palace made for stark symbolism -- an opposition leader had removed such portraits from the same building
Former Vice President Elias Jaua evoked Bolivar and Chavez as he kicked off one of the supporters' marches to the palace.
"Let us go with God, with Bolivar, with our commander Hugo Chavez," Jaua said. "Chavez lives! Chavez lives!"
Opponents of Maduro's regime, on the other hand, were expected to gather at various points in Caracas in the afternoon, intending to march toward the palace.
Meanwhile, the opposition-led assembly indicated it would continue meeting in the palace -- raising prospects that two camps may claim to be the country's legitimate government
"The National Assembly will continue doing (its) work in the Federal Legislative Palace as 14 million of Venezuelans ordered it on December 6, 2015," the assembly tweeted.
Opposition leader returns to house arrest
Hours before the new assembly's inauguration, an imprisoned political opponent of Maduro's was released to house arrest.
Antonio Ledezma, one of two opposition figures whom authorities took from their homes Tuesday
, was placed back under house arrest early Friday, his wife, Mitzy Capriles, said in a series of tweets.
The other opposition figure, Leopoldo Lopez, remained in jail.
"Antonio said he comes back with concern that Leopoldo and more than 600 political prisoners continue behind bars," Capriles tweeted on her husband's account Friday.
Ledezma, a former Caracas mayor, and Lopez, a former mayor of the Caracas district of Chacao, had been under house arrest for separate allegations. Ledezma was arrested in 2015 on suspicion of being involved in a plot to overthrow the government, and Lopez was convicted that year of being behind a deadly anti-regime protest.
The two were taken to jail Tuesday after both publicly opposed Sunday's election in videos posted to social media.
Venezuela's Supreme Court said the men were taken because intelligence officials claimed they were planning to flee.
Voter fraud allegations
The National Electoral Council announced that more than 8 million people -- about 41.53% of registered voters -- went to the polls Sunday, but allegations of voter fraud quickly emerged.
, which has provided voting technology for Venezuela since 2004, said the turnout figures were manipulated.
Smartmatic CEO Antonio Mugica said his company stood by all previous results but this time, it noticed a discrepancy of at least 1 million votes between the officially declared tally and what the firm recorded.
A full audit will be needed, he said.
Maduro disputed the allegations and blasted Mugica; however, Venezuela's attorney general launched an investigation
into potential voter fraud within hours.
Attorney General Luisa Ortega Diaz told CNN en Español that two prosecutors are investigating four of five directors of the National Electoral Council "for this very scandalous act that could generate more violence in the country than what we have already experienced."
On Thursday, US State Department spokeswoman Heather Nauert said the United States won't recognize Venezuela's National Constituent Assembly because "the process was rigged from the start" and "the election lacked credible international observation."
Months of strife
Maduro is aligned with the political movement of Chavez, Venezuela's President from 1999 until his death in 2013.
Chavez trumpeted a brand of socialism -- dubbed Chavismo -- in which he increased subsidies to the poor and fixed prices for goods but alienated Venezuela from foreign investors who were spooked by his anti-American rhetoric. Chavez chose Maduro to succeed him as interim President, and he narrowly won election in December 2013.
Venezuela became dependent on selling its oil abroad, and income suffered when the price of oil per barrel dropped from $100 in 2014 to $26 in 2016. Inflation has soared, and unemployment could reach 25% this year, according to the International Monetary Fund.
For months, Venezuela has struggled with the collapsing economy and a standoff between Maduro and the opposition. His opponents wanted to impeach him after they won a National Assembly majority in 2015, but he stacked the Supreme Court with his supporters, blocking any impeachment attempts.
The Supreme Court briefly attempted to dissolve the National Assembly in March, sparking a wave of nearly daily protests. More than 120 people have been killed in the ongoing unrest.