The inauguration follows Maduro's controversial win last year in an election that was largely boycotted by the opposition and criticized by the United States, European Union and others as a "sham".
The 56-year-old socialist leader was sworn in at the Supreme Court before an audience of hundreds, rather than the sidelined, opposition-controlled National Assembly, before heading to a ceremony at Venezuela's military academy.
"I swear on behalf of the people of Venezuela ... I swear on my life," Maduro said as he took the oath of office. After being presented with the presidential sash, Maduro turned to salute the crowd.
Maduro's new mandate will keep him at the helm of the oil-rich, cash-strapped country until at least 2025.
The opposition called for protests during the ceremony, while thousands of pro-Maduro flooded the streets.
Several countries have said they will not recognize Maduro's new mandate.
With the exception of Mexico, the Lima Group - made up of 14 Latin American countries and Canada - has urged Maduro to cede power to the National Assembly until new elections can be held.
The Organization of American States (OAS) similarly backed a resolution declaring Maduro's government illegitimate at a special session to discuss the situation in Venezuela and Nicaragua.
On Thursday, US National Security Adviser John Bolton tweeted that the US would not recognize "the Maduro dictatorship's illegitimate inauguration"
"We will continue to increase pressure on the corrupt regime, support the democratic National Assembly, and call for democracy and freedom in Venezuela," he said in a tweet.
Shortly after, US Secretary of State Mike Pompeo condemned what he called Maduro's "usurpation of power".
Just minutes after Maduro was sworn in, Paraguayan President Mario Abdo Benitez said he was cutting diplomatic ties with Venezuela and immediately withdrawing his country's diplomats.
Peru also recalled its charge d'affaires in protest, according to the Peruvian foreign ministry.
Representatives from Bolivia, Cuba, El Salvador, Nicaragua and the disputed territory of South Ossetia were slated to attend the swearing-in, along with those of Maduro's main international backers China, Russia and Turkey.
In a lengthy press conference on Wednesday, Maduro hit out at the US and the Lima Group, accusing them of directing a coup against his "legitimate and constitutional" government, adding that the government is ready to "confront and thwart any traitors who intend violence against Venezuela".
A former bus driver and union leader, Maduro was the handpicked successor of Venezuela's late leftist leader Hugo Chavez.
Since taking office in 2013, Maduro has consolidated power by gaining control of virtually all the country's institutions and instigating a systematic crackdown on dissent.
Many blame him for Venezuela's economic woes, which have seen soaring hyperinflation and widespread shortages of food and medicine.
The situation is set to worsen, with the International Monetary Fund (IMF) predicting that inflation will hit a staggering 10,000,000 percent in 2019.
More than three million people have fled the country since the crisis began in 2015, according to the United Nations, in what has become Latin America's largest-ever migration.
The flow of migrants and refugees into neighboring countries has raised tensions in the region, with neighboring countries, most vocally Brazil and Colombia, calling for regime change in Venezuela.
Washington has also slapped several rounds of sanctions on high-ranking Venezuelan officials and businesses.
Despite the dire domestic situation and increasing international pressure, the ongoing support of the armed forces effectively ensures Maduro's position is secure.
The country's opposition has attempted several legal means to dislodge the president, without success. It is seen by many as too fractured to take on Maduro, who has forced many prominent leaders into exile.
In a press conference following the inauguration, the President of the National Assembly Juan Gerardo Guaido Marquez, said the body would not recognize any decisions taken by Maduro's administration and asked the military to join the National Assembly in defending Venezuela's constitution.
In response to the opposition's call for protests, authorities filled the streets with police checkpoints and heavily-armed troops.
While protests over high prices and food shortages are commonplace, there have been few wide-scale political demonstrations since massive protests over the sidelining of the National Assembly in 2017 left more than 100 people dead.
However Venezuelans in several countries including Brazil and Colombia are demonstrating against the inauguration.
A recent survey by the country's most reliable pollster found that almost 72 percent of people want Maduro to resign, rather than begin his second term.