Donald Trump is the first former US president to go on trial after being charged with 34 felonies for falsifying corporate documents.
Following his formal arrest earlier on Tuesday, Mr. Trump made an appearance in a Manhattan court and entered a not-guilty plea.
The accusations are related to a purported hush-money payment made to a porn star in the lead-up to the 2016 presidential election, as was expected.
In this case, Mr. Trump, 76, has denied any misconduct.
After being arraigned, Mr. Trump departed the courthouse with an expressionless face. On Tuesday night, he is anticipated to fly directly back to his Mar-a-Lago estate in Florida, where he has scheduled a speech for 20:15 local time (01:15 BST).
The issue revolves around an alleged $130,000 (£105,000) payment made to adult film star Stormy Daniels by his former lawyer Michael Cohen before the 2016 presidential election.
Three additional investigations are centered on the former president and include his handling of confidential papers after leaving the White House as well as efforts to get the 2020 election results annulled.
The payment, which Mr. Cohen claimed he made at the request of Mr. Trump when he was still a candidate, was purportedly intended to silence Ms. Daniels about an affair she allegedly had with Mr. Trump. Mr. Trump has denied ever having sex with Ms. Daniels.
Although hush money deals are lawful, Manhattan district attorney Alvin Bragg is looking into whether any company records were tampered with in connection with the payment.
The chances of a conviction are now unknown, but the accusations against Mr. Trump, who has already started his third presidential campaign, have thrust the nation into uncharted political waters.
Although a criminal conviction wouldn’t stop Mr. Trump from running for president or from retaking the White House, the protracted legal battle may prove to be a significant distraction for the Republican front-runner and cause additional confusion in his party’s primary.