The Constituent Assembly, elected last weekend in a vote marred by violence and allegations of fraud, will sit in a chamber in the Legislative Palace in Caracas, where the opposition-controlled legislature is located.
The inaugural session of its 500-plus members -- including Maduro's wife and son -- will take place under high security.
The opposition has called a mass march in the capital against the body, raising fears of violence that could add to a death toll of more than 125 over the past four months.
The United States, the European Union and major Latin American nations have said they will not recognize the assembly.
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The Vatican on Friday urged that the new assembly be suspended, saying it was one of several initiatives that "foment a climate of tension." It also appealed for Venezuelan security forces to show restraint.
Meanwhile, Venezuela's intelligence service unexpectedly transferred a high-profile opposition figure, Caracas mayor Antonio Ledezma, from jail back to house arrest, his family said.
Lopez remains incarcerated, one of hundreds of people who the opposition says are political prisoners.
The Constituent Assembly marks a new stage in Venezuela's rule.
With unlimited powers to dissolve the National Assembly or amend laws, the new body is tasked with rewriting the 1999 constitution brought in under Maduro's late mentor and predecessor, Hugo Chavez.
Maduro claims the revised charter will yank Venezuela out of its political and economic crisis, though he has not detailed how. Nor has he given an end date for the Constituent Assembly, which he said would operate for years.