Police had earlier said the Florida man was being viewed as ‘sort of a conspiracy theorist’.
On Saturday, the New York City police department said the man, identified as Max Azzarello of St Augustine, Florida, was declared dead at a local hospital where he was taken for treatment after the incident on Friday.
Police said the man, who was born in 1987, did not appear to be targeting Trump or others involved in the trial.
During the incident, which took place on Friday, the fourth day of Trump’s trial on criminal charges of falsifying business records, Azzarello threw pamphlets in the air before using an alcohol-based cleaning substance to douse himself and light the fire.
Police had said earlier that he was being viewed “as sort of a conspiracy theorist”.
Trump, the first former US president to face criminal charges, is on trial in connection with hush-money payments he allegedly made to adult film star Stormy Daniels.
Many police officers were present at the scene on Friday as part of the extensive security precautions to ensure the safety of the trial.
Journalists from across the world were also waiting outside the court, and some were live on air when Azzarello self-immolated.
Police had said the man had not breached any security checkpoints to access the park across from the court, and that he had recently travelled from Florida to New York.
Authorities said following the incident that they are reviewing security protocols and considering shutting down access to the park where Azzarello set himself ablaze. The side street where Trump enters and leaves the building is off-limits to everyone.