Holt read a message sent by Greenwald expressing his support.
During the town hall, Holt said the National Security Agency's approach to surveillance goes against what the United States should be about.
"It turns the basic principles of this country on its head," said Holt, adding that he supports the repeal of the Patriot Act. "It treats Americans as suspects first and citizens second."
Holt, who touts himself as a scientist and a progressive, is running against U.S. Rep. Frank Pallone, Assembly Speaker Sheila Oliver, and Booker, Newark's mayor, for the Democratic nomination. Holt, Pallone, and Oliver trail Booker in polls.
On the Republican side, Steve Lonegan, former mayor of Bogota, faces physician Alieta Eck. The primary election takes place Aug. 13, followed by the special election Oct. 16.
Holt spent much of the night advocating liberal viewpoints, including a single-payer health-care system and a carbon tax to help curb climate change.
"Climate change is real and humans are to blame," Holt said in a campaign video aired at the town hall.
"The risks of adverse climate change are very real," said former Secretary of Energy Steven Chu, adding that the country should be a leader in utilizing renewable energy. "We can lead in this transition to a sustainable world."
Holt also advocated for a broader immigration policy, which he said would benefit the country in more than just financial ways. By doing so, "we're going to have a country that's richer culturally, socially, and economically in the future," he said.
Though he showed support for compromise, Holt said he would not compromise facts when crafting legislation.
"We shouldn't lower our sights," the congressman said. "We should hold out for our vision of what America should be."
Contact Sean Carlin at 856-779-3237, firstname.lastname@example.org, or follow on Twitter @SeanCarlin84.