Christian Zerpa's embarrassing defection came days before Maduro begins his second term amid calls from critics and the international community to relinquish power.
Zerpa on Monday accused Venezuela's high court of becoming a tool of Maduro's inner circle, lacking any judicial independence since he and a group of ruling party members were appointed to the bench in 2015.
"Nicolas Maduro doesn't know the constitution, and he doesn't know the laws," Zerpa said in a Florida news conference. "This has no other name than a dictatorship."
Maduro is expected to take his oath of office on Thursday before the Supreme Court, launching his second, six-year term.
Political opponents and many foreign nations consider it illegitimate, saying his re-election in May was a sham because popular opponents were banned from running and the largest anti-government parties boycotted the race.
Zerpa said that he fled with his family because he didn't want to play a role legitimizing Maduro's rule. Relatives staying behind have since been visited by Venezuela's intelligence police, he said.
"Maduro is incompetent," Zerpa said. "The country and it public companies are in ruins."
In far-reaching comments, Zerpa said the military lacks a national conscience for allowing Maduro stay in power, and he accused Supreme Court chief justice Maikel Moreno of having ties with drug traffickers.
Zerpa didn't provide evidence, holding back sensitive information, but said that he's ready to cooperate with a sweeping U.S. investigation into corruption and human rights abuses among Venezuela's well-connected.
Maduro loyalist Moreno said Sunday that Zerpa fled Venezuela to escape allegations of sexual harassment charges lodged by women in his office. Zerpa denied Moreno's claims.
Zerpa surfaced publicly in Miami on Sunday, describing how he received directions from the influential first lady Cilia Flores on how to rule in politically sensitive cases.
The key ruling cemented Maduro's power, preventing the opposition from amassing a two-third super majority that would have severely curtailed Maduro's power.
Zerpa apologized for propping up Maduro's government as long as he did, saying that he feared being jailed as a dissident where his life would be put at risk.
"I will not be able to return to Venezuela," Zerpa said. "I am a dead man."
Zerpa is among the top Venezuelan officials who have been sanctioned by Canada, but he has not been targeted by U.S. authorities, who accuse dozens in Maduro's administration of using their power for personal gain.
Pressure has been mounting against Maduro internationally and from his political opponents still inside Venezuela.
A dozen Latin American governments and Canada delivered a blistering rebuke Friday, rejecting the legitimacy of Maduro's second term and urging him to hand over power as the only path to restoring democracy.
The opposition-led congress on Saturday opened its session for the year vowing to battle against Maduro's socialist administration.
Maduro says he intends to take the oath despite his critics and press ahead with the socialist revolution, promising a turnaround of the failing economy.
"The revolution is stronger today than ever, more experienced than ever, to defend the sovereignty of the country," he said. "Venezuelans have the opportunity to enjoy 2019 as a year of prosperity and progress."
Opposition lawmaker Julio Borges, who lives in exile fearing for his safety, sent a letter Monday to the leaders of Latin American nations. He urged Mexico and Spain to join the broad effort to help return Venezuela to democratic rule.
"The inhuman arrogance of this dictatorship led by Nicolas Maduro personally challenges the heads of state of the region," Borges said. "It's not fair that a whole country should perish to satisfy one man's lust for power."