Police have identified the man as Maxwell Azzarello, in his mid-30s, from St. Augustine in Florida.
He is now in a critical condition in hospital after setting himself alight in a designated protest area for pro and anti-Trump demonstrators.
The NYPD said it has opened an investigation after its officers responded to the fire at around 1:37pm local time (6:37pm UK time).
Mr Azzarello took a canister out of his bag containing what is believed to have been an alcohol-based accelerant, before dousing himself in the fluid and setting himself ablaze, police said.
Officers and civilians ran into the protest area and attempted to put out the flames using coats and fire extinguishers, NYPD Chief of Department Jeff Maddrey told reporters.
Four police officers suffered minor injuries from fire exposure, authorities said.
NYPD Chief of Detectives Joseph Kenny told reporters: "The pamphlets appear to be propaganda-based, almost a conspiracy theory type of pamphlet. Some information in regards to a Ponzi scheme and the fact that some of our local educational institutes are fronts for the mob. So, a little bit of a conspiracy theory going on here."
The blaze broke out after jury selection for Trump's hush money trial concluded with 12 people, and six alternatives, chosen to decide whether the former US president covered up payments to women who alleged they had affairs with him.
The Trump campaign released a statement this afternoon offering its "condolences to the traumatised witnesses" after the blaze.
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Karoline Leavitt, the national secretary for his campaign, said: "Not knowing the motivations behind this sickening situation, it's difficult to make any definitive remarks, other than to say we are thankful that to the best of our present knowledge, nobody other than the individual in question was hurt."
She added: "Today is more proof that our nation is in deep trouble... Make America Great Again."
Footage shared on social media shows Mr Azzarello lying on his back on the pavement outside the courthouse while the lower part of his body is on fire.
Another man sprays him with a fire extinguisher which appears to put the fire out.
Police officers are seen running over to the scene as the fire is extinguished.
Freelance photojournalist Ed Quinn was outside the court at the time and told Sky News' US partner network NBC News: "I heard someone scream 'He's going to light himself on fire!'.'
"I see him dumping gasoline on his face, very deliberately.
"He had a grey T-shirt on. It soaked his face. It soaked his shirt. Boom, he went up."
Mr Quinn said it took the police about a minute to arrive.
He continued: "Women were begging, screaming, put it out, put him out."
Trump facing multiple charges in historic trial
Hours after the jury members were decided on Friday, an appeals court judge rejected a last-minute bid by Trump to halt the trial over his claims that the jury selection process was unfairly rushed.
The judge also said he would not consider Trump's immunity motion that was filed just before the hush money trial began.
Opening statements in the trial are scheduled to take place on Monday.
In what is the first criminal trial of a former US president, Trump is accused of criminally altering business records to cover up a $130,000 (£104,200) payment to adult film actress Stormy Daniels, real name Stephanie Clifford, during his 2016 election campaign.
Ms Daniels and former Playboy model Karen McDougal, who was paid $150,000 (£120,000), both claim to have had affairs with Trump.
His lawyers say the payment was meant to spare himself and his family embarrassment, not help him win the election.
Trump is facing 34 felony counts of falsifying business records and could get up to four years in prison if convicted.
He is also facing three other criminal cases that could go to trial.
Trump has pleaded not guilty to all charges.
In court today, one prospective juror was excused after saying she suffers from anxiety and felt she could struggle to be impartial, while another was called to the judge's bench after bursting into tears.
The first woman said she takes medication and that as the days go on "I don't think I will be able to be completely fair".
The second broke down crying and, according to Sky News' partner NBC News, said: "I have to be honest, I feel so nervous and anxious right now. I'm sorry."
"I thought I could do this... I don't want you to feel like I've wasted anyone's time," she added before being called to the bench and excused.

A video showed an officer using the term while speaking to Gideon Falter, chief executive of the Campaign Against Antisemitism, who was wearing a kippah skull cap near the demonstration in the Aldwych area of London on the afternoon of Saturday 13 April.
Issuing an apology on behalf of the Met on Saturday, Assistant Commissioner Matt Twist said the officer's use of the phrase was "hugely regrettable" but added that the issues surrounding the ongoing protests are "complex, contentious and polarising".
In a statement which included the apology, the assistant commissioner added: "In recent weeks we've seen a new trend emerge, with those opposed to the main protests appearing along the route to express their views.
"The fact that those who do this often film themselves while doing so suggests they must know that their presence is provocative, that they're inviting a response and that they're increasing the likelihood of an altercation.
"They are also making it much more likely officers will intervene.
"They don't do so to stifle free speech or to limit the right to protest, but to keep opposing groups apart, to prevent disorder and keep the public - including all those taking part in or opposing the protest - safe."
Mr Twist added that the the video, which was shared by the Campaign Against Antisemitism, will "further dent the confidence of many Jewish Londoners".
'Victim-blaming'
Mr Falter has responded to Mr Twist's remarks by accusing the force of "victim-blaming".
In a statement posted on the X social media platform, he wrote: "What has dented Jewish Londoners' confidence in the Met is not us making this video public, but the actions of the Met's officers telling me that I cannot be in the area whilst openly Jewish.
"The assistant commissioner appears to be saying that we should have taken this on the chin and kept the video under wraps.
"Not only that, but whilst apologising for the behaviour of his officers, he then doubles down on their language by saying that the presence of people like me - Jews - is 'provocative'."
Mr Falter added that it is his right and "the right of every Jew" to walk freely around London.
He continued: "If police threaten us with arrest for doing so or consider our presence to be a provocation, then the Met has decided wholesale to curtail the rights of Jews in order to appease lawless mobs".
"On Saturday 27th April, I and hopefully others will again walk in our home city, again being 'quite openly Jewish'. We must not be intimidated by protesters or prevented by police from exercising our rights."
Further police apology
The Met Police have since deleted their Tweet and issued an apology for any offence caused.
Their statement reads: "The use of the term "openly Jewish" by one of our officers is hugely regrettable. We know it will have caused offence to many. We reiterate our apology.
"We have reflected on the strength of the response to our previous statement. In an effort to make a point about the policing of protest we have caused further offence. This was never our intention. We have removed that statement and we apologise."
How did the row start?
Mr Falter said he was walking in the capital after attending a synagogue and was not there to counter-protest as he walked past the demonstration last Saturday.
The video clip shows one police officer saying to him: "You are quite openly Jewish, this is a pro-Palestinian march, I'm not accusing you of anything but I'm worried about the reaction to your presence."
In the clip another officer said to him: "There's a unit of people here now.
"You will be escorted out of this area so you can go about your business, go where you want freely or if you choose to remain here because you are causing a breach of peace with all these other people, you will be arrested."
The officer said that Mr Falter's presence was "antagonising".
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The antisemitism campaigner said after the incident: "Despite being told repeatedly that London is safe for Jews when these marches are taking place, my interactions with police officers last Saturday show that the Met believes that being openly Jewish will antagonise the anti-Israel marchers and that Jews need protection, which the police cannot guarantee.
"Instead of addressing that threat of antisemitic violence, the Met's policy instead seems to be that law-abiding Jewish Londoners should not be in the parts of London where these marches are taking place. In other words, that they are no-go zones for Jews."
Tens of thousands of pro-Palestinian protesters had gathered in London last Saturday to call for a ceasefire and to urge the government to stop all arms sales to Israel.
Crowds waved Palestinian flags, chanted "free Palestine" and held signs calling for a "ceasefire now".

Ibrahim Moussawi, a Hezbollah spokesperson, also warned Israel "will see results" if they continue provoking Iran.
"Nobody has an interest in going into an open confrontation, comprehensive war in the region, because this might lead to other things. This is not because the Western side has an awakening of humanity or whatever," he said.
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"This is because it doesn't boil down to their interest, it does not suit their policies.
"At the same time, we don't want, as well, to have a comprehensive confrontation from our side. But if it is imposed, they see and we will see the kind of results that will unfold."
Mr Moussawi added: "If things escalated into a larger scale, everybody has to understand that just like what the West is doing, all of these governments and armies and countries supplying Israel, then the Axis [of Resistance] will fight as an Axis.
"I believe if the Israelis put us in a position or any situation where we have to manifest this again, they will see it [Iran and Hezbollah's military capacity]."
Speaking about a possible end to hostilities in the region, Mr Moussawi said the responsibility lies with the West.
"In order to reach an agreement, they have to stop the aggressor. They have to stop Netanyahu and this bunch of idiots who are in the occupied Palestine to stop their genocidal war.
"Then you'll see clearly that the fronts will come down," he said.
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He also blamed Western countries for escalating the crisis in the region and claimed they are complicit in the humanitarian situation in Gaza.
"If you want to see things go into calmness again, go stop the Israeli aggression. You have the way to stop the Israeli aggression," he said.
"You know, I know, everybody knows that they wait for the military ammunitions and supplies from the United States, from the West, to continue to kill the children and women in Gaza.
"No one in the Western governments is ready to stop supplying Israel with ammunitions, and at the same time, they drop what they call a few portions of food on the heads of the people and they kill them, and at the same time they send rockets to Israel to kill them.
"This is a complete fiasco - it does not work."
Mr Moussawi's comments come after an Israeli strike close to a major military airbase and a nuclear site near the central city of Isfahan this morning.
He played down the strikes against Iran, saying he has "never heard of such a thing" and he had "heard it in the news".
"My understanding is that the Israelis, up till now, they want to save their face," he said.

Outlining his plans to reform the welfare system if the Conservatives win the next general election, Rishi Sunak said "unemployment support should be a safety net, never a choice" as he promised to "make sure that hard work is always rewarded".
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Mr Sunak said his government would be "more ambitious about helping people back to work and more honest about the risk of over-medicalising the everyday challenges and worries of life" by introducing a raft of measures in the next parliament. They include:
• Removing benefits after 12 months for those deemed fit for work but who do not comply with conditions set by their work coach - such as accepting a job offer
• Tightening the work capability assessment so those with less severe conditions will be expected to seek employment
• A review of the fit note system to focus on what someone can do, to be carried out by independent assessors rather than GPs
• Changes to the rules so someone working less than half of a full-time week will have to look for more work
• A consultation on PIP to look at eligibility changes and targeted support - such as offering talking therapies instead of cash payments
• The introduction of a new fraud bill to treat benefit fraud like tax fraud, with new powers to make seizures and arrests.
He insisted the changes were not about making the benefits system "less generous", adding: "I'm not prepared to balance the books on the backs of the most vulnerable.
"Instead, the critical questions are about eligibility, about who should be entitled to support and what kind of supports best matches their needs."
But Labour said it was the Tories' handling of the NHS that had left people "locked out" of work, and a disabled charity called the measures "dangerous".
The latest data from the Office for National Statistics (ONS) shows 9.4 million people aged between 16 and 64 were "economically inactive", with over 2.8 million citing long-term sickness as the reason.
Mr Sunak said 850,000 of them had been signed off since the COVID pandemic and half of those on long-term sickness said they had depression, with the biggest growth area being young people.
He also claimed the total being spent on benefits for people of working age with a disability or health condition had increased by almost two-thirds since the pandemic to £69bn - more than the entire budget for schools or policing.
"I will never dismiss or downplay the illnesses people have," said the prime minister. "Anyone who has suffered mental ill health or had family and friends who have know these conditions are real and they matter.
"But just as it would be wrong to dismiss this growing trend, so it would be wrong to merely sit back and accept it because it's too hard, too controversial, or for fear of causing offence."
The prime minister said he knew critics would accuse him of "lacking compassion", but he insisted "the exact opposite is true", adding: "There is nothing compassionate about leaving a generation of young people to sit in the dark before a flickering screen, watching as their dreams slip further from reach every passing day.
"And there is nothing fair about expecting taxpayers to support those who could work but choose not to.
"It doesn't have to be like this. We can change. We must change."
But Labour said the "root cause of economic activity" was down to the Tories' failure on the health service, with record NHS waiting lists hitting people's ability to get back in the workplace.
Acting shadow work and pensions secretary Alison McGovern said: "After 14 years of Tory misery, Rishi Sunak has set out his failed government's appalling record for Britain: a record number of people locked out of work due to long-term sickness and an unsustainable spiralling benefits bill.
"Rather than a proper plan to get Britain working, all we heard today were sweeping questions and reheated proposals without any concrete answers."
Liberal Democrat leader Sir Ed Davey called it "a desperate speech from a prime minister mired in sleaze and scandal", adding: "Rishi Sunak is attempting to blame the British people for his own government's failures on the economy and the NHS and it simply won't wash."
Meanwhile, disability charity Scope said the measures were a "full-on assault on disabled people", adding they were "dangerous and risk leaving disabled people destitute".
James Taylor, director of strategy at the charity, said calls were already "pouring in" to their helpline with people concerned about the impact on them, adding: "Sanctions and ending claims will only heap more misery on people at the sharp end of our cost of living crisis."

Mr Menzies, the MP for Fylde in Lancashire, gave up the Tory whip in the wake of reports in The Times that he misused party funds. He disputes the allegations.
The allegations came about after Mr Menzies former campaign manager, Katie Fieldhouse, spoke to the newspaper.
In a new interview with The Times this evening, Ms Fieldhouse, 78, claims she was told the Conservative Party was aware the allegations were potentially criminal.
She says the Conservative Party's chief of staff "told me that when they first took over the investigation [from the Whips' Office] they had consulted solicitors".
She added: "He told me on the phone, 'the solicitor said it is fraud but you are not duty-bound to report it because it's not Conservative Party money'."
The whistleblower said she was told the decision not to inform the police was made because it was donors' money and not the party's.
A Conservative spokesperson said: "The party is conducting an investigation into the claims made and has been doing so for several months.
"We will of course share any information with the police if they believe it would be helpful to any investigation they decide to undertake.
"Suggestions the party has not been seriously examining this matter are demonstrably false."
Lancashire Police said today it was "reviewing" information about Mr Menzies after Labour asked for an investigation to take place.
In a statement, the force said: "We can confirm that we have now received a letter detailing concerns around this matter and we are in the process of reviewing the available information in more detail."
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The party's chief whip, Simon Hart, is said to have been made aware of the claims in January, when the former campaign manager reported what had happened.
Sky News understands there has been an investigation ongoing by Conservative Campaign Headquarters (CCHQ) since the allegations were first raised, but further information came to light this week and Mr Hart acted immediately.
Speaking tonight, Labour's chair Anneliese Dodds said: "The Conservative chairman and chief whip must urgently come out of hiding and explain what they knew and what advice they received.
"If, as reported, they or Conservative officials? were warned about potentially fraudulent activity and chose not to go to the police, this would be indefensible."
Mr Menzies, who has served as an MP since May 2010, is reported to have phoned his 78-year-old former campaign manager at 3.15am last December, saying he was locked in a flat by "bad people" and needed £5,000 as a matter of "life and death".
The sum, which rose to £6,500, was eventually paid by his office manager from her personal bank account and subsequently reimbursed from funds raised from donors in an account named Fylde Westminster Group, the newspaper says.
Speaking to Sky News, Ms Fieldhouse said: "I am feeling dreadful because I am a devout Tory and as I have said to everybody else, I reported his actions to the chief whip… it is now the middle of April.
"Come to your own conclusions [about] what is happening."
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Asked if she was disappointed with the way the complaint was being handled, she said: "Yes."
Mr Menzies said on Thursday: "I strongly dispute the allegations put to me. I have fully complied with all the rules for declarations. As there is an investigation ongoing I will not be commenting further."