Judge Arthur Engoron, ruling in a civil lawsuit brought by New York’s attorney general, found that the former president and his company deceived banks, insurers and others by massively overvaluing his assets and exaggerating his net worth on paperwork used in making deals and securing financing.

Engoron ordered that some of Trump’s business licenses be rescinded as punishment, making it difficult or impossible for them to do business in New York. The judge also said he would continue to have an independent monitor oversee the Trump Organization’s operations.

A Trump spokesperson did not immediately respond to a request for comment on the ruling. Trump has long insisted he did nothing wrong.

The decision is the strongest repudiation yet of Trump’s carefully coiffed image as a wealthy and shrewd real estate mogul turned political powerhouse.

Beyond mere bragging about his riches, Trump, his company and key executives repeatedly lied on his annual financial statements, reaping rewards such as favourable loan terms and lower insurance premiums, Engoron found.

Those tactics crossed a line and violated the law, the judge said, rejecting Trump’s contention that a disclaimer on the financial statements absolved him of any wrongdoing.

“In defendants’ world: rent regulated apartments are worth the same as unregulated apartments; restricted land is worth the same as unrestricted land; restrictions can evaporate into thin air; a disclaimer by one party casting responsibility on another party exonerates the other party’s lies,” Engoron wrote in his 35-page ruling. “That is a fantasy world, not the real world.”

Manhattan prosecutors had looked into bringing a criminal case over the same conduct but declined to do so, leaving New York Attorney General Letitia James to sue Trump and seek penalties that could disrupt his and his family’s ability to do business in the state.

Engoron’s ruling – which comes in a phase of the case known as summary judgement – resolves the key claim in James’s lawsuit, but six others remain.

Engoron is slated to hold a non-jury trial starting October 2 before deciding on those claims and any punishments he may impose. The trial could last into December, Engoron has said.

Trump’s lawyers had asked the judge to throw out the case, which he denied. They contend that James was not legally allowed to file the lawsuit because there is no evidence the public was harmed by Trump’s actions. They also argued that many of the allegations in the lawsuit were barred by the statute of limitations.

Engoron, noting that he had “emphatically rejected” those arguments earlier in the case, equated them to the “time-loop in the film Groundhog Day”.

James, a Democrat, sued Trump and the Trump Organization a year ago, alleging a pattern of duplicity that she dubbed “the art of the steal”, a twist on the title of Trump’s 1987 business memoir The Art of the Deal.

The lawsuit accused Trump and his company of routinely inflating the value of assets like skyscrapers, golf courses and his Mar-a-Lago estate in Florida, padding his bottom line by billions.

Among the allegations was that Trump claimed his Trump Tower apartment in Manhattan – a three-story penthouse replete with gold-plated fixtures – was nearly three times its actual size and valued the property at $327m. No apartment in New York City has ever sold for close to that amount, James said.

Trump also valued Mar-a-Lago as high as $739 million – more than 10 times a reasonable estimate of its worth. Trump’s figure for the private club and residence was based on the idea that the property could be developed for residential use, but deed terms prohibit that, James said.

Trump has denied wrongdoing, arguing in sworn testimony for the case that it did not matter what he put on his financial statements because they have a disclaimer that says they should not be trusted. He told James at the April deposition, “You don’t have a case and you should drop this case.”

“Do you know the banks were fully paid? Do you know the banks made a lot of money?” Trump testified. “Do you know I don’t believe I ever got even a default notice, and even during COVID, the banks were all paid? And yet you’re suing on behalf of banks, I guess. It’s crazy. The whole case is crazy.”

Engoron rejected that argument when the defence previously sought to have the case thrown out.

The judge said the disclaimer on the financial statements “makes abundantly clear that Mr Trump was fully responsible for the information contained within” them. He also said that “allowing blanket disclaimers to insulate liars from liability would completely undercut” the “important function” that such statements serve.

James’s lawsuit is one of several legal headaches for Trump as he campaigns for a return to the White House in 2024. He has been indicted four times in the last six months.

In two of those indictments – one in Georgia, one in Washington, DC – he stands accused of plotting to overturn his 2020 election loss. In Florida, meanwhile, he has been charged with hoarding classified documents and in Manhattan, he is accused of falsifying business records related to hush money paid on his behalf.

The Trump Organization was convicted of tax fraud last year in an unrelated criminal case for helping executives dodge taxes on extravagant perks such as Manhattan apartments and luxury cars. The company was fined $1.6m.

One of the executives, Trump’s longtime finance chief Allen Weisselberg, pleaded guilty and served five months in jail. He is a defendant in James’s lawsuit and gave a sworn deposition testimony for the case in May.

James’s lawsuit does not carry the potential of prison time but could complicate Trump’s ability to transact real estate deals. It could also stain his legacy as a developer.

James has asked Engoron to ban Trump and his three eldest children from ever again running a company based in New York. She also wants Trump and the Trump Organization barred from entering into commercial real estate acquisitions for five years, among other sanctions. The $250m in penalties she is seeking is the estimated worth of benefits derived from the alleged fraud, she said.

James, who campaigned for office as a Trump critic and watchdog, started scrutinising his business practices in March 2019 after his former personal lawyer Michael Cohen testified to Congress that Trump exaggerated his wealth on financial statements provided to Deutsche Bank while trying to obtain financing to buy the NFL’s Buffalo Bills.

James’s office previously sued Trump for misusing his charitable foundation to further his political and business interests. Trump was ordered to pay $2m to an array of charities as a fine.

The charity, the Trump Foundation, was shut down.