The decision by Justice Arthur Engoron came in state Attorney General Letitia James' $250 million lawsuit accusing the Republican former president, his company and three of his children of over-valuing assets and Trump's net worth through a decade of lies to banks and insurers.
Last month, James asked the Manhattan-based judge to appoint an independent monitor to halt ongoing fraud at the company and keep the Trumps from transferring assets out of her reach.
Engoron called appointing a monitor "the most prudent and narrowly tailored mechanism to ensure there is no further fraud or illegality," citing "persistent misrepresentations" in Trump's statements of financial condition from 2011 to 2021.
Trump blasted what he called Engoron's "ridiculous" decision, one day after suing James, a Democrat, in a Florida court to stop what Trump labeled her "inquisition."
"A puppet judge of the New York Attorney General and other sworn enemies of President Trump and the Republican Party has just issued a ruling never before seen anywhere in America," Trump said. "It is Communism come to our shores."
Separately, the Trump Organization referred to next week's midterm elections in saying the decision "sets a dangerous precedent for government interference in private enterprise and is an obvious attempt to influence the outcome of the upcoming election."
The decision bars the defendants from transferring assets without court approval, and requires that the monitor receive a "full and accurate description" of the Trump Organization's structure and assets.
Engoron said his skepticism was bolstered by Trump's decision to invoke his constitutional right against self-incrimination more than 400 times when questioned under oath by James' office in August.
In a statement, James called the decision a "major victory" that will stop Trump and his companies from continuing "the extensive fraud that we uncovered." She also noted that the judge found her claims likely to succeed at trial.
Both sides have until Nov. 10 to recommend three candidates to become a monitor.
The judge's decision focused on several alleged instances of fraud, including Trump's claim that his penthouse apartment atop Manhattan's Trump Tower was nearly triple its actual size, giving it an inflated $327 million valuation in 2015. No apartment in Manhattan has sold for that much.
"You said experts can disagree" on valuation, the judge told Christopher Kise, a lawyer for Trump at a hearing on Thursday. "But does there reach a point it's just not a disagreement ... but bad faith?"
Kise argued that James' demand for a monitor was a "manufactured emergency" ahead of next Tuesday's midterm election.
He said James had no legal authority to challenge how Trump valued his properties, calling it a private matter between Trump's company and its lenders and insurers.
"There's just no public interest here at all," Kise said, calling the alleged fraud a matter of "corporate titans versus corporate titans."
Kevin Wallace, a lawyer from James' office, countered that it was important to the public to maintain an "honest and fair business environment" in the state.
"The alternative is, we're in the wild, wild west," he said.
The Trump Organization manages hotels, golf courses and other real estate around the world.
James sued the company and Trump's family in September, following a more than three-year probe.
The case is among many legal battles Trump faces as he mulls a 2024 bid for the presidency.
Testimony also began this week in another Manhattan courtroom in a criminal case by the Manhattan district attorney's office accusing the Trump Organization of scheming to defraud tax authorities for at least 15 years.
That trial went on hold after the first witness tested positive for COVID-19 on Tuesday.