A former member of Guyana's parliament and another man were convicted of plotting to blow up jet fuel tanks at John F Kennedy International Airport in a plan authorities said was intended to dwarf the September 11, 2001 attacks.
Russell Defreitas, a former JFK cargo handler, and Abdul Kadir, were convicted of multiple conspiracy charges. Kadir was acquitted of one charge, surveillance of mass transportation.
The verdicts came after the Brooklyn federal court jury deliberated for about five days.
Defreitas, a 66-year-old naturalised US citizen from Guyana, and Kadir, 58, a former member of parliament, were arrested in 2007 after an informant infiltrated the plot and recorded them discussing it.
Prosecutors said Defreitas and Kadir wanted to kill thousands of people and cripple the American economy by using explosives to blow up the fuel tanks and the underground pipelines that run through an adjacent Queens neighbourhood.
Authorities say the men sought the help of militant Muslims, including an al-Qaida operative, in Guyana.
The defendants wanted to set off an explosion "so massive ... that it could be seen from far, far away", assistant US attorney Zainab Ahmad said in closing arguments. Their vision prompted them to codename the plot The Shining Light, he said.
During the trial the men's lawyers described them as clueless rubbish-talkers led astray by the informant, a convicted drug dealer.
"There's more than just the evidence Mr Kadir was coming up against," his lawyer, Kafahni Nkrumah, said. "There's the atmosphere of fear in the country ... of Muslims, Islam and fear of terrorists, especially in New York City."
Defreitas' lawyer Mildred Whalen said there would not have been a case without the US government's intervention.
"I think it was clear these guys couldn't act on their own ... and didn't act on their own," she said. "We're deeply disappointed."
But US attorney Loretta Lynch praised the work of the investigators.
"The defendants intended to send a message by killing Americans and destroying the New York City economy," she said.
"Today, the only message is that those who engage in potentially deadly plots against the US will be stopped and punished."
Both defendants who face life in prison when they are sentenced on December 15, plan to appeal.
Prosecutors relied heavily on the informant's secret recordings, which captured Defreitas bragging about his knowledge of Kennedy Airport and its vulnerabilities.
In other tapes he ranted about punishing the US with an attack that would "dwarf 9/11" and told the informant his US citizenship gave him cover.
"They don't expect nobody in this country to do something like this," he said. "They have their eyes on foreigners, not me."
Kadir gave evidence in his own defense, denying he was a militant Muslim who spied for Iran for years before joining the JFK scheme.
He told jurors that he warned the plotters: "Islam does not support aggression or killing innocent people."
As part of the plot, Defreitas and the informant travelled to Guyana, a predominantly Asian Indian country on South America's Caribbean coast, to try to meet Kadir and show him home-made videotapes of the airport's so-called fuel farms.
The plotters also discussed reaching out to Adnam Shukrijumah, an al Qaida member, FBI-most wanted terrorist and explosives expert, who was believed to be hiding out in the Caribbean at the time.
Shukrijumah was indicted in federal court in Brooklyn this month on charges that he was involved in a failed plot to attack the New York City tube system with suicide bombers.
Another man, Abdel Nur, pleaded guilty to a lesser charge in the case and is awaiting sentencing.
The case of a fourth suspect, Kareem Ibrahim, was severed from the others' after he fell ill. It's not clear when he would be tried.