After two days of deliberation, the 12-member jury pronounced Trump guilty on all 34 counts he faced.
Trump watched the jurors dispassionately as they were polled to confirm the unanimous verdict.
Justice Juan Merchan set sentencing for July 11, just days before the Republican Party is expected to nominate Trump for president ahead of the Nov. 5 election.
Trump faces a maximum sentence of four years in prison, though others convicted of that crime often receive shorter sentences, fines or probation. Incarceration would not prevent him from campaigning, or taking office if he were to win.
He will not be jailed ahead of sentencing.
Merchan thanked the jurors for their service and told them they were free to speak about their experience on the jury if they wished. "Nobody can make you do anything you don’t want to do. The choice is yours," Merchan said.
The verdict plunges the United States into unexplored territory ahead of the November vote, when Trump will try to win back the White House from Democratic President Joe Biden.
Trump, 77, has denied wrongdoing and was expected to appeal.
"This was a disgrace," Trump told reporters afterwards as he proclaimed his innocence and repeated his complaints that the trial had been rigged against him.
"The real verdict is going to be Nov. 5 by the people," he said.
Trump gave a thumbs-up sign through the tinted window of his SUV as his motorcade left the courthouse.Trump supporters stood in a park opposite the courthouse along with journalists, police and onlookers.
Opinion polls showTrumpand Biden, 81, locked in a tight race, and Reuters/Ipsos polling has found that a guilty verdict could costTrumpsome support among independent and Republican voters.
The jury found Trump guilty of falsifying business documents after sitting through a five-week courtroom presentation that featured explicit testimony from porn star Stormy Daniels about a sexual encounter she says she had with Trump in 2006 while he was married to his current wife Melania. Trump denies ever having sex with Daniels.
Trump's former fixer Michael Cohen testified that Trump approved a $130,000 hush money payment to Daniels in the final weeks of the 2016 election, when he faced multiple accusations of sexual misbehavior.
Cohen testified that he handled the payment, and that Trump approved a plan to reimburse him through monthly payments disguised as legal work.
Trump's lawyers hammered Cohen's credibility, highlighting his criminal record and imprisonment and his history of lying. Merchan also cautioned jurors to examine his testimony carefully.
The relatively short amount of time jurors needed to reach a verdict was a sign that they thought there was enough evidence to back up Cohen's testimony, said George Grasso, a retired New York judge who attended the trial.
A source familiar with the Trump campaign's inner workings said the verdict was expected to prompt him to intensify deliberations on picking a woman as his vice presidential running mate. His campaign website labeled him a "political prisoner" and urged supporters to donate.